Help find a >=25A continuous battery for Bafang BBS02 750W

[gameofbikes]

I am looking for a battery to pair with the BBS02 750W I'm about to order. I'm located in the US and my state allows this motor.

Use cases
Daily commute (~5mi each way). I live in a hilly area, with some of the hills being very steep. I also want to lug 2-3 bags of groceries home up a big hill. For the steepest hill, which my home happens to be on top of, I cannot pedal up the hill myself, I always have to walk the bike up. I'm moderately fit, and weigh 165lbs. Living on this hill is a big negative incentive for me getting out and about, because I always think about how grueling the trip home will be.

About 75% of my commute to school will be mostly flat, or mild 2% slopes. For those flatter portions I will probably use just enough assist to offset the extra weight of the ebike kit/battery/cargo, plus maybe a little extra oomph. So probably pedal assist setting in the 3-4 range (out of 9). I will always pedal at least at a moderate effort level.

Form Factor / Packaging:
I prefer something that mounts to the frame, like one of the bottle bracket mounted ones. I don't like the big triangle packs, I find they look ugly on the bike and they would be too awkward to carry around when I lock my bike up. Small rear saddle bags (the kind that hang off the back, just under the seat) would be good but I don't think they could carry enough battery, though I could be wrong about that.

Battery Tech / Safety
I'm new to the ebike world, but from what I see, people are buying lithium polymer cells from hobbyking and putting them in bags. I don't want to deal with anything that has a risk of burning down my home if I make a simple mistake, so I don't think those lippo's are for me. I store the bike in my living room, and I don't want something with exposed wires and stuff there. I also am on a limited budget (~$500, though even that much is more than I thought I would spend, but I think my previous budget was unrealistic). I will be in school for the next 3 years and would like the battery to last that entire time. So based on my desire for safety and long life, I think LiFePO4 would be suitable. Are there other suitable chemistries based on my needs?

I wouldn't mind something DIY, as long as the end result is safe, wires are hidden from sight, reliable, and lasts 2-3 years (~2,800 miles / year). Is there some DIY option that would be suitable for me with minimal risk of fire/explosion?

Battery Specs
Because I need the bike to be able to carry loads, and to carry those loads up hills, I want to be able to max out the motor, which means 48V, and at least 25A continuous discharge. High speeds aren't that important to me. My commute is about 4.7 miles each way, so I think a 9Ah might do the trick, but a little extra for longer trips would be welcome, so i'm looking for the range of 9-15Ah. I don't know how fast I go currently, but probably average, so I'm guessing 18-22mph would be a good target speed. What batteries would you suggest that fit all the above criteria?

I have done quite a bit of research already, so I'm not coming here empty handed:

I'm finding it quite hard to locate a downtube mounted battery that meets these specs. I've found some on aliexpress, but I don't know if the vendors are reliable. The thing that's extra infuriating about them is even if they have good vendor ratings, they often do things like have two different sets of specs on the same page that contradict each other, and sometimes both of those contradict info in the product listing title. That doesn't instill confidence, as I have no way of knowing what to expect.

I looked at e3mv's batteries based on Paul's reputation for high quality. I think the product info on his downtube batteries is outdated since it doesn't have any info about the 25R based batteries, and there is one part i find confusing. Does anyone know the rated discharge, and max continuous discharge of the various batteries on this page: http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161 ?

And the part that confuses me is this:

Discharge Current, recommended 20A continuous (BMS Limited, see following suggestions regardfing specific cell types).

Does this mean all the batteries have a discharge rate that is limited? Does he configure the BMS limited discharge rates different based on the cells? I emailed him about these two things using the "Contact Us" link on his site, but haven't gotten a response yet. Is there a better way to contact Paul?

Em3ev seems like the best option, but they are by far the most expensive. When you include shipping, em3ev batteries $/Ah cost is easily cost 2-3x more than most of what I find on aliexpress. I created an excel sheet with batteries, specs, urls, vendor reputation, Ah. $/Ah, Ah/kg, etc for tons of different places including conhismotors, em3ev, lots of different aliexpress vendors, and a few other retailers who are based in or ship to the USA. If anyone is interested in that sheet let me know and I'll send it over. Side note: I think it would be cool to see a public battery buying guide with that type of info, that ES members could update on a regular basis.

Update 2015-01-05:
Got a reply from Paul @em3ev:

The 25R cells are simply a high capacity and high power cell. It performs like the 20R, but has significantly greater capacity.

I have now added some additional info to the listing which mentions the 25R cells. I’ve copied this below. The BMS is the limiting factor in these packs when using the higher power 20 and 25R cells. The 20R or 25R cells are able to deliver 80A in a 4 parallel configuration, but the BMS is rated to just 20A continuous.
<snip>...
The high Power 20R and 25R packs can deliver 30A or more, but we recomemnd the continuous discharge rate is kept to 25A to avoid stressing the BMS.

Still seems like this battery shouldn't run up a steep hill for more than a few seconds, as the BMS is apparently rated for 20A.

 

[DAND214]

The one I know you can trust is Paul.
Prices are usually better than others after the shipping added. What you will find with E3ev is the shipping listed is what you pay.

If you emailed Paul, you have to wait a few days.
He is very busy.

Most of the BOTTLE battery packs are under your demands. I think Paul might be able to rectify that problem.

The triangle pack is not a big problem to carry, it comes with a shoulder strap. hardest part is the Velcro.

Dan

 

[melodious]

If you live in the foothills or mountains, I'd stay away from the 29E cells, dependent on your parallel configuration. I get mild sag on heavy loads on my 10s 6p 16Ah bottle battery. It may trigger LVC sooner in more hilly terrain. It will trigger sooner if you get a battery with less Ah of 29E cells, like the 11Ah pack Paul sells. Stick with higher C rated cells for the bottle batteries, but the large triangle batteries shouldn't matter what cell you choose.

You could ask Paul to limit the BBS-2 Amps from 25 to 18-20, especially if your more than adequate cyclist already. Just gear the bicycle right and your golden.

 

[oobagooba]

Does anyone know the rated discharge, and max continuous discharge of the various batteries on this page: [em3ev]

I emailed him about these two things using the "Contact Us" link on his site, but haven't gotten a response yet. Is there a better way to contact Paul?

1. Go to this page, scroll down to the last 4 paragraphs for the specs. http://em3ev.com/store/index.php?route=product/product&path=35&product_id=158


2. Be patient. Otherwise you'll get gray hairs over this nascent technology of power-assisting bicycles across oceans and cultures.

 

[gameofbikes]

Does anyone know the rated discharge, and max continuous discharge of the various batteries on this page: [em3ev]

I emailed him about these two things using the "Contact Us" link on his site, but haven't gotten a response yet. Is there a better way to contact Paul?

1. Go to this page, scroll down to the last 4 paragraphs for the specs. http://em3ev.com/store/index.php?route=product/product&path=35&product_id=158


2. Be patient. Otherwise you'll get gray hairs over this nascent technology of power-assisting bicycles across oceans and cultures.

I was asking about a different battery pack. I'm not sure if this page is has the info I want. I do see specs on that one for the 25R, but I don't know if the bottle mounted pack with the 25R has the same BMS and same discharge specs. Do they? If so, how do you know there isn't something different between the two? I'm asking because I'm new to this stuff, not sarcasm.

 

[spinningmagnets]

From Pauls page on his bottle mount pack:

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161

The high Power 20R pack can deliver 30A or more, but we recommend the continuous discharge rate is kept within reasonable limits to avoid stressing the BMS. This is not a high power battery pack, at least not by EM3ev standards.

Although the 25R is listed as an option, the data page has not been updated yet to include it. I am sure Paul can include a BMS that is set to 25A using that cell, but I suppose you will have to wait for his reply. The 25R cell in a 4P configuration should easily be able to provide 25A continuous without stress, from what I have read.

Have you considered one of his small triangle packs? Perhaps they allow a physically larger BMS that is less heat-sensitive? The one I have contains the 30A BMS.

 

[gameofbikes]

From Pauls page on his bottle mount pack:

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161

The high Power 20R pack can deliver 30A or more, but we recommend the continuous discharge rate is kept within reasonable limits to avoid stressing the BMS. This is not a high power battery pack, at least not by EM3ev standards.

Although the 25R is listed as an option, the data page has not been updated yet to include it. I am sure Paul can include a BMS set to 25A using that cell, but I suppose you will have to wait for his reply. The 25R call in a 4P configuration should easily be able to provide 25A continuous without stress, from what I have read.

Have you considered one of his small triangle packs? Perhaps they allow a physically larger BMS that is less heat-sensitive? The one I have contains the 30A BMS.

Actually, I didn't realize that the two triangle packs were different sizes. I'm not a big fan of the way the triangles look, though I do like that they put the weight in the middle rather than in back. They also support my Amp req's with the right cells. The cost per Ah is pretty high: $62.24 & $69.96 $/Ah for the 25R and 20R cells respectively (including shipping to my state in the US).

There are a few non-Aliexpress batteries with much better $/Ah:
17.6Ah, 40A continuous,25.52$/Ah,6.2kg long brick style aluminum case. But this one is too long (18.9") to fit on my bike's downtube: http://conhismotor.com/ProductShow.asp?id=462

20Ah, 50A continuous, $26.40/Ah, 6.0kg raw pack (guess I'd get a rear rack & bag to hold it): https://bmsbattery.com/ebike-battery/673-high-c-rate-48v20ah-li-ion-battery-heat-shrink-battery-pack-battery.html

IIRC the reputation of both seem hit or miss based on posts I've read here. I've seen enough good feedback on bms that i'd take the chance though. So far this is the most likely one I'd get. Anyone know a very compact and waterproof way of carrying this pack inside the frame? Pref. a small rectangular pack on the cross tube? What about on rear rack?

 

[Ade]

This is where I got my 25R 10ah frame battery and there's some info there; http://www.custom-ebikes.com/48v-10ah-high-power-samsung-25r-cell-pack/
I think it's probably very similar to what you'd get from Em3ev. So far, impressive output on my Bafang 750w mid drive going uphill.

 

[tln]

20Ah, 50A continuous, $26.40/Ah, 6.0kg raw pack (guess I'd get a rear rack & bag to hold it): https://bmsbattery.com/ebike-battery/673-high-c-rate-48v20ah-li-ion-battery-heat-shrink-battery-pack-battery.html

IIRC the reputation of both seem hit or miss based on posts I've read here. I've seen enough good feedback on bms that i'd take the chance though. So far this is the most likely one I'd get. Anyone know a very compact and waterproof way of carrying this pack inside the frame? Pref. a small rectangular pack on the cross tube? What about on rear rack?

Bmsbattery has a high c-rate 10ah battery that will save $ and space. Unless you think you need super long range?

Rear rack is the easiest option for a brick like that IMO although front rack might leave you better balanced and with more cargo capacity in the rear

You've done an impressive amount of research! Just how steep is your hill? You might want to consider lower gears on your bike if its really steep.

 

[cycborg]

Does anyone have experience with the BBS02 at 1250 W continuous? I’d be seriously concerned about the controller under those conditions, given Paul’s reports of fried controllers from the programming thread (see discussion starting here and in particular this post from Paul).

There’s one stretch of my commute where I use about 850 W to pull me up a 3-4% grade at 30 kph for 2 minutes. This is about 17 battery amps, which is about the most I’m comfortable pulling continuously from my 10 Ah Ping LiFePO4. But if I had a battery with higher current rating, going beyond this would cause me to worry about my controller. I think 25 A bursts are fine for both battery and controller, but I wouldn’t want to sit there for long.

 

[gameofbikes]

From Pauls page on his bottle mount pack:

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=161

The high Power 20R pack can deliver 30A or more, but we recommend the continuous discharge rate is kept within reasonable limits to avoid stressing the BMS. This is not a high power battery pack, at least not by EM3ev standards.

Although the 25R is listed as an option, the data page has not been updated yet to include it. I am sure Paul can include a BMS that is set to 25A using that cell, but I suppose you will have to wait for his reply. The 25R cell in a 4P configuration should easily be able to provide 25A continuous without stress, from what I have read.

Have you considered one of his small triangle packs? Perhaps they allow a physically larger BMS that is less heat-sensitive? The one I have contains the 30A BMS.

If you own the small triangle pack, would you mind posting a pic of it mounted to a bike? I looked at the dimensions and it seems they might be compact enough that I wouldn't mind the look of it.

 

[scfoster]

Don't know if you can recharge for each leg of the commute or whether you have to do a round trip to recharge. That makes a significant difference... obviously.

My commute is 5.5 miles each way with a few significant hills. That was what got me looking for an ebike in first place.

Here was my order with em3ev

46.8V (13S) Samsung Frame Pack & Charger (8.2-11.0Ah)
- Configuration: 13S 4P, 25R cells, 47V, 9.8Ah
Sub-Total: $499.00
Shipping - Battery - Fed Zone 1/2 (Weight: 5.50kg): $118.70
PayPal fee: $22.85
Total: $640.55

I can easily do 3 trips 16.5 miles with high pedal assist and use of full throttle from standing starts at stop lights; many of those starts are on hills.

25-30 mph is normal on long duration flats/slight downslopes. 18mph is typical on upslope with high PAS. It takes me 18 minutes to get to work, with traffic, stoplights, partial sidewalk riding, etc. so the average speed is 18 mph.

I asked Paul for his recommendation after sending him my riding parameters. I've been happy so far.

 

[mwkeefer]

Hello,

I read your thread and just wanted to make you aware of something...

I have and run a BBS02 with external controller but did about 3K with internal and on a calibrated CA peak for a second or less was 25A but it quickly dropped down to about 20A continuous. I successfully ran a simple 48v 13AH All Cell pack with Zero issues on flats or massive hills like I have up my road.

So continuous needs to be around 20A rated and peak somewhere between 25A and 30A for 1-3 seconds maximum.

Hope this helps!

-Mike

 

[tln]

Does anyone have experience with the BBS02 at 1250 W continuous? I’d be seriously concerned about the controller under those conditions, given Paul’s reports of fried controllers from the programming thread (see discussion starting here and in particular this post from Paul).

There’s one stretch of my commute where I use about 850 W to pull me up a 3-4% grade at 30 kph for 2 minutes. This is about 17 battery amps, which is about the most I’m comfortable pulling continuously from my 10 Ah Ping LiFePO4. But if I had a battery with higher current rating, going beyond this would cause me to worry about my controller. I think 25 A bursts are fine for both battery and controller, but I wouldn’t want to sit there for long.

I regularly pull 26A for 5-6 minutes going up a 16% grade hill at about 9mph. The other day my pedal broke and I used throttle only all the way up at about 7mph, 7 minutes. FWIW the motor wasn't hot after that either.

Posting on the main thread may give you more anecdata

 

[scfoster]

Posting on the main thread may give you more anecdata

"Anecdata" I love that word!! Almost as good as "Administrivia"

hijack off.....

 

[Ch00paKabrA]

Reading from your initial post, I would recommend being very careful on AlliExpress. I buy a lot of stuff there and the best way to do it is to never buy anything from a vendor with no feedback. A while back I was looking into batteries and there were a number of vendors who had battery packs that were listed for around 1/2 of what others had listed them. They had no feedback so I decided to wait and see if some of the orders that were pending left feedback. On every single occasion, the product stopped selling and the listing disappeared once the vendor hit 10 or 15 orders. So, those really good deals on AliExpress are usually a scam. The legit vendors are actually close in price to EM3EV so it is worth it, in my opinion to go with a tried and true vendor.

I live in a flat area with just a few hills and run the 29E cells and they do sag fairly badly once I do hit the rare hill. There is one hill that I now do not even attempt. I just walk the bike up it. I tried to get the 25R cells off of AliExpress but after 2 attempts from 2 different vendors I gave up and bought the 29E cells states side. Fortunately for me, I did get a refund as the sellers just did not have the inventory on hand to meet the order; they were scammers in every sense of the word.

Good luck

 

[gameofbikes]

Reading from your initial post, I would recommend being very careful on AlliExpress. I buy a lot of stuff there and the best way to do it is to never buy anything from a vendor with no feedback. A while back I was looking into batteries and there were a number of vendors who had battery packs that were listed for around 1/2 of what others had listed them. They had no feedback so I decided to wait and see if some of the orders that were pending left feedback. On every single occasion, the product stopped selling and the listing disappeared once the vendor hit 10 or 15 orders. So, those really good deals on AliExpress are usually a scam. The legit vendors are actually close in price to EM3EV so it is worth it, in my opinion to go with a tried and true vendor.

I live in a flat area with just a few hills and run the 29E cells and they do sag fairly badly once I do hit the rare hill. There is one hill that I now do not even attempt. I just walk the bike up it. I tried to get the 25R cells off of AliExpress but after 2 attempts from 2 different vendors I gave up and bought the 29E cells states side. Fortunately for me, I did get a refund as the sellers just did not have the inventory on hand to meet the order; they were scammers in every sense of the word.

Good luck

What battery do you use right now? Why didn't you order the 25R or 20R from em3ev, price?

 

[oobagooba]

I was asking about a different battery pack. I'm not sure if this page is has the info I want. I do see specs on that one for the 25R, but I don't know if the bottle mounted pack with the 25R has the same BMS and same discharge specs. Do they? If so, how do you know there isn't something different between the two? I'm asking because I'm new to this stuff, not sarcasm.

I think he uses the same cells just builds them into bigger or smaller packs. Sounds like he may be too busy to update every page every time he gets a new cell like the 25r. So if you can read up on the individual cells from his site, you could do the math re. whatever size pack you're considering. That way it saves on time with the email exchange across time zones, etc. He also talks about the BMS:

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=158
"For effortless High Discharge Capabilities, choose the 20R Pack which can deliver 5C plus discharge rates without strain. The 20R Pack can easily delivery 40A continuous or more, but is limited to 40A Continuous by the BMS, although the BMS can easily deliver much more extended bursts.
The 20R Pack is limited more by the BMS than the Cells themselves and should be considered if being used with a controlleer with greater than 25A rating."


I think the 25r is even higher discharge. Maybe Paul can program the BMS for you and recommend which pack.


http://em3ev.com/store/index.php?route=product/product&path=35&product_id=123
"The 20R cell is 10C rated and will effortlessly deliver 5C plus discharge rates. If long term continuous dischrarge rate is close to or exceeding 40A, the high power 20R cells (10C Rated) should be considered. With a 20R pack, the BMS is the limiting factor. A 20R equipped pack with circa 17.5Ah can easily deliver 80A or more. The 20R delivers High Current effortlessly, with little voltage sag and also tends to maintain a higher voltage at the end of the discharge, with a flatter discharge curve."

Another thing to consider with Paul's batteries, is they will probably be built much better than a "mystery" Chinese pack, and he stands behind his work. Not to mention all the info on his site. Does BMSbattery say what kind of chemistry is in their "high discharge battery"? I don't know. I think with them "you are the quality control." Good luck!

 

[tomjasz]

As compatible battery solution I would suggest 2 X 12S Headway 38120L or 38120S if you have the money.
If you do not have the money, the decision for 750W was wrong from the start.

http://www.ittsb.eu/forum/index.php?topic=959.0

Again with the stick. Why keep poking riders with the same tired line. You have a nice ride, let others enjoy theirs. Repeatedly telling others they made a mistake serves no purpose other than inflating the ego. A waste of time.

I tried mounting my batteries on a rear rack and it's anything but the ideal location, especially given the weight of the headway batteries. Now don't get me wrong, I respect your choice but your choice is not the only way and has definitely different ride characteristics with a rear mount. It throws the balance off and negates some of the advantage of the mid motor. FOR ME. You should incorporate that phrase. FOR YOU. Opinions are like butt holes we all have one. :lol:

Let people ride what they ride, answer the request as asked. Not try to convince us your way is better. It's not it's just different.

 

[tomjasz]

I am very pleased with my EM3ev battery. Lectric sold me theirs claiming it was superior. It was more expensive so in that sense it was better, but the EM3ev battery gives better performance at a lower price. Support is every bit as good. As it has turned out, the support from Paul is better. I worry about a problem. With Paul I don't worry. Consistently excellent support. Just a day or two delay in communication. Others have waited frustratingly long for conhis and BMS. EM3ev for fair dollars and sense.

 

[gameofbikes]

As compatible battery solution I would suggest 2 X 12S Headway 38120L or 38120S if you have the money.
If you do not have the money, the decision for 750W was wrong from the start.

http://www.ittsb.eu/forum/index.php?topic=959.0

Again with the stick. Why keep poking riders with the same tired line. You have a nice ride, let others enjoy theirs. Repeatedly telling others they made a mistake serves no purpose other than inflating the ego. A waste of time.

I tried mounting my batteries on a rear rack and it's anything but the ideal location, especially given the weight of the headway batteries. Now don't get me wrong, I respect your choice but your choice is not the only way and has definitely different ride characteristics with a rear mount. It throws the balance off and negates some of the advantage of the mid motor. FOR ME. You should incorporate that phrase. FOR YOU. Opinions are like butt holes we all have one. :lol:

Let people ride what they ride, answer the request as asked. Not try to convince us your way is better. It's not it's just different.

I was thinking of starting a thread to ask about battery placement. If I'm riding on city streets does it matter if the battery is in the rear rack? I have read on here that people don't like it on the rack. Are those people doing some special type of riding, like offroad or mountain biking? I've never ridden a bike with any cargo in the back, so I wouldn't think that 10-15lbs back there would be so terrible. After all, some carry a bunch of stuff in panniers and baskets back there.

Are there any options besides triangle packs that will mount one a heatshrink wrapped battery pack?

 

[gameofbikes]

As compatible battery solution I would suggest 2 X 12S Headway 38120L or 38120S if you have the money.
If you do not have the money, the decision for 750W was wrong from the start.

http://www.ittsb.eu/forum/index.php?topic=959.0

Cool, thanks for your opinion.

This is the first I've seen Headway mentioned. Looks like they are a type of cell rather than a battery pack maker/assembler, is that correct?

 

[gameofbikes]

I was asking about a different battery pack. I'm not sure if this page is has the info I want. I do see specs on that one for the 25R, but I don't know if the bottle mounted pack with the 25R has the same BMS and same discharge specs. Do they? If so, how do you know there isn't something different between the two? I'm asking because I'm new to this stuff, not sarcasm.

I think he uses the same cells just builds them into bigger or smaller packs. Sounds like he may be too busy to update every page every time he gets a new cell like the 25r. So if you can read up on the individual cells from his site, you could do the math re. whatever size pack you're considering. That way it saves on time with the email exchange across time zones, etc. He also talks about the BMS:

http://em3ev.com/store/index.php?route=product/product&path=35&product_id=158
"For effortless High Discharge Capabilities, choose the 20R Pack which can deliver 5C plus discharge rates without strain. The 20R Pack can easily delivery 40A continuous or more, but is limited to 40A Continuous by the BMS, although the BMS can easily deliver much more extended bursts.
The 20R Pack is limited more by the BMS than the Cells themselves and should be considered if being used with a controlleer with greater than 25A rating."


I think the 25r is even higher discharge. Maybe Paul can program the BMS for you and recommend which pack.


http://em3ev.com/store/index.php?route=product/product&path=35&product_id=123
"The 20R cell is 10C rated and will effortlessly deliver 5C plus discharge rates. If long term continuous dischrarge rate is close to or exceeding 40A, the high power 20R cells (10C Rated) should be considered. With a 20R pack, the BMS is the limiting factor. A 20R equipped pack with circa 17.5Ah can easily deliver 80A or more. The 20R delivers High Current effortlessly, with little voltage sag and also tends to maintain a higher voltage at the end of the discharge, with a flatter discharge curve."

Another thing to consider with Paul's batteries, is they will probably be built much better than a "mystery" Chinese pack, and he stands behind his work. Not to mention all the info on his site. Does BMSbattery say what kind of chemistry is in their "high discharge battery"? I don't know. I think with them "you are the quality control." Good luck!

The "high C Rate" ones I'm considering from BMSBattery are Li-NiCoMn. I think I remember seeing the chem for all the ones I looked at on their site.

 

[gameofbikes]

Hello,

I read your thread and just wanted to make you aware of something...

I have and run a BBS02 with external controller but did about 3K with internal and on a calibrated CA peak for a second or less was 25A but it quickly dropped down to about 20A continuous. I successfully ran a simple 48v 13AH All Cell pack with Zero issues on flats or massive hills like I have up my road.

So continuous needs to be around 20A rated and peak somewhere between 25A and 30A for 1-3 seconds maximum.

Hope this helps!

-Mike

What's the benefit of using an external controller? I didn't know that was possible with the bbs02.

 

[gameofbikes]

As compatible battery solution I would suggest 2 X 12S Headway 38120L or 38120S if you have the money.
If you do not have the money, the decision for 750W was wrong from the start.

http://www.ittsb.eu/forum/index.php?topic=959.0

Cool, thanks for your opinion.

This is the first I've seen Headway mentioned. Looks like they are a type of cell rather than a battery pack maker/assembler, is that correct?

Basically Headway is the company with a cells product range including the larger LIFEPO4 which is the latest generation of Lipo.
LIFEPO4 comes with far improved specifications and a single 38120 is capable 10Ah nominal which at that specification you get the 5-7 years life cycle or 2000 charges.
When you need higher current you add too chains of them so to still qualify for 5-7 years life cycle or 2000 charges.

Any one having buy all ready older technology that is these 18650 cells, he does feel negatively charged, but my note is for people who care about getting the best in 2015.
And as you can see the specific 38120 cells are so easily serviceable too.
In the battle between past and future? My vote goes to future, simple as that.

Yes, I usually go for newer technology, especially if it means something will last longer. I didn't know that 38120 cells were newer than 18650, I thought it was just a different size but same tech. That is good to know as well. I haven't seen a lot of those during the research I've been doing (mostly 18650 & polymer pouches so far). I will be reading more about Headway & 38120 cells.

Also, is it a good idea to mix partially used batteries with new ones? Does that cause any problems? For example, if I need more current in the future as you mentioned, it wouldn't be a problem to add more new cells in parallel to the ones I've already been using?

Thanks!