HK Lipo Bricks - what do I choose and why?

[Allex]

This is LiPo thread, but ok we can do a comparison.
I agree that lipos are modular, and you can easily connect them how you like it. But you can do the same with cylindrical cells, but this will requeire some work preparing them in modules with connectors.

As for space and weight here are some calculations(please correct me if I am wrong).
If we take one of the best 18650 in terms of energi density (Sanyo GA 3,6V 3,5Ah) we get that you can fit:
GA 12.6Wh 18x650mm total: 16.54CC 0,76Wh/cm3
0,76Wh per cubic centimeter

Then we can take the new and popular Multistar High Capacity 4S 8000mAh we get that you can fit:
MS 118,4Wh 142x49x43mm total: 299.194cc 0,4Wh/cm3
0,4Wh per cubic centimeter

I had to count above several times because the figures differs by a lot! You can almost fit twise as much energy in the same space.

How about Wh/kg?
GA:
12,6Wh/45g=0,28wh/g or 280Wh/kg
Multistar Lipo:
118.4Wh/643g=0,184wh/g or 184Wh/Kg

Same thing here, you get 96Wh more or less for each kg
And its is up to you to decide weather it is worth to carry 2kg of 560Wh or 2kg of 368Wh


But lets take those popular hard case packs, they are really horrible in terms of power density and you can almost compare them to Lead acid when taking 18650 into account
http://www.hobbyking.com/hobbyking/store/__26801__Turnigy_5000mAh_4S1P_14_8v_20C_Hardcase_Pack_UK_Warehouse_.html?strSearch=turnigy%20hardcase

These babies have 0,268wh/cm3 or 140Wh/Kg

So if you want a 1000Wh battery, the question would be weather it is ok for you to carry those 7Kg of cardcases or could it maybe be better to invest in 3,6kg of 18650?
But of course, if the price your main concern, then go for lipo, or?
What about USD/Wh?

Hardcase is about 2,9Wh/USD 345Bucks for 1000Wh (you need connectors and cables to connect them)
GA is about 2,52Wh/USD 398Bucks for 1000Wh (but then you need spot welder[soldering iron works fine, my pack still works perfectly after a year] and nickel strip)

Again guys, please correct me if I am wrong here somewhere!

 

[Ykick]

This is LiPo thread, but ok we can do a comparison.
I agree that lipos are modular, and you can easily connect them how you like it. But you can do the same with cylindrical cells, but this will requeire some work preparing them in modules with connectors.

As for space and weight here are some calculations(please correct me if I am wrong).
If we take one of the best 18650 in terms of energi density (Sanyo GA 3,6V 3,5Ah) we get that you can fit:
GA 12.6Wh 18x650mm total: 16.54CC 0,76Wh/cm3
0,76Wh per cubic centimeter

Then we can take the new and popular Multistar High Capacity 4S 8000mAh we get that you can fit:
MS 118,4Wh 142x49x43mm total: 299.194cc 0,4Wh/cm3
0,4Wh per cubic centimeter

I had to count above several times because the figures differs by a lot! You can almost fit twise as much energy in the same space.

How about Wh/kg?
GA:
12,6Wh/45g=0,28wh/g or 280Wh/kg
Multistar Lipo:
118.4Wh/643g=0,184wh/g or 184Wh/Kg

Same thing here, you get 96Wh more or less for each kg
And its is up to you to decide weather it is worth to carry 2kg of 560Wh or 2kg of 368Wh


But lets take those popular hard case packs, they are really horrible in terms of power density and you can almost compare them to Lead acid when taking 18650 into account
http://www.hobbyking.com/hobbyking/store/__26801__Turnigy_5000mAh_4S1P_14_8v_20C_Hardcase_Pack_UK_Warehouse_.html?strSearch=turnigy%20hardcase

These babies have 0,268wh/cm3 or 140Wh/Kg

So if you want a 1000Wh battery, the question would be weather it is ok for you to carry those 7Kg of cardcases or could it maybe be better to invest in 3,6kg of 18650?
But of course, if the price your main concern, then go for lipo, or?
What about USD/Wh?

Hardcase is about 2,9Wh/USD 345Bucks for 1000Wh (you need connectors and cables to connect them)
GA is about 2,52Wh/USD 398Bucks for 1000Wh (but then you need spot welder[soldering iron works fine, my pack still works perfectly after a year] and nickel strip)

Again guys, please correct me if I am wrong here somewhere!

My eyes glaze over when algebraic numbers, values and formulas begin appearing out of thin air. But from what I can see from your calculations based on 1000Wh pack there’s probably a good argument to be made.

Basic trouble for me with your illustration is that I rarely need or bother with 1000Wh eBike pack. 300Wh is usually plenty for my purposes.

For that I regularly buy the hobby lipo stuff in your example for under $110 USD shipped. I see 2-3 years service from em, I’m pretty happy with that. You should know, Hobby RC Lipo series connect just fine with the supplied 4mm bullets. Connectors only really become issue when you parallel series groups. Which I rarely do, FYI…

I do get the can cell support, I really do. And I hope supply/services improve to provide us with HR (high rate) assemblies which can be affordably configured and assembled into eBike battery packs.

Some of you have solved it and I’m sure you’re happy with your evolution. We’ll get there, but please understand it’s not always as “simple” or “easy” as it may appear to be from other position(s).

 

[Allex]

Well, I took the numbers from HK and GA cells spec sheet, so nothing to worry about there. I do agree that it is more work to get a working 36V pack out of 18650 cells compared to just snap a few lipos in series!

 

[macribs]

This is LiPo thread, but ok we can do a comparison.

If we take one of the best 18650 in terms of energi density (Sanyo GA 3,6V 3,5Ah) we get that you can fit:
GA 12.6Wh 18x650mm total: 16.54CC 0,76Wh/cm3
0,76Wh per cubic centimeter

Then we can take the new and popular Multistar High Capacity 4S 8000mAh we get that you can fit:
MS 118,4Wh 142x49x43mm total: 299.194cc 0,4Wh/cm3
0,4Wh per cubic centimeter



How about Wh/kg?
GA:
12,6Wh/45g=0,28wh/g or 280Wh/kg
Multistar Lipo:
118.4Wh/643g=0,184wh/g or 184Wh/Kg

Same thing here, you get 96Wh more or less for each kg
And its is up to you to decide weather it is worth to carry 2kg of 560Wh or 2kg of 368Wh


But lets take those popular hard case packs, they are really horrible in terms of power density and you can almost compare them to Lead acid when taking 18650 into account
http://www.hobbyking.com/hobbyking/store/__26801__Turnigy_5000mAh_4S1P_14_8v_20C_Hardcase_Pack_UK_Warehouse_.html?strSearch=turnigy%20hardcase

These babies have 0,268wh/cm3 or 140Wh/Kg

Wow that was a compelling argument you made. I don't think I ever have looked at the like this before. Well you just got me hooked Allex. 18650 it is.
Off to learn about spot welding, pack design, strip size and so much more......sigh a little overwhelmed right now, big task ahead for one uneducated old timer new to the world of electric, physics and electrons.

 

[Ykick]

Well, I took the numbers from HK and GA cells spec sheet, so nothing to worry about there. I do agree that it is more work to get a working 36V pack out of 18650 cells compared to just snap a few lipos in series!

And what is GA?

 

[Allex]

ncr18650ga from Panasonic/Sanyo, latest cell on the block which seems to be used in the latest 2016 Teslas.
I do build packs with this cell from time to time.


Ribs, Will you ever build that bike of yours? New stuff keep coming in so it is hard to settle right? Haha!

 

[Ykick]

ncr18650ga from Panasonic/Sanyo, latest cell on the block which seems to be used in the latest 2016 Teslas.
I do build packs with this cell from time to time.

So GA isn't like HK = HobbyKing? We gotta break some code now?

Do you understand how frustrating this shit gets to be? Frock it, I can open HK website select, pay and have something shipped today that I can put to work in minutes. Plenty cheap and lightweight enough.

 

[Allex]

haha, Do you remember when you got to the bike world, how it was frustrating then, million of options
But it is about the same with 18650, choose your distributor and hit the order button or email them.

 

[macribs]

Hm how cheap can I be and still get fast acceleration from the QS 205 hub? I will need to spend cash also on spot welder, car battery, nickel strips, etc.

My plan was 20s14p. But do to weak currency at the moment this will be too expensive if I choose top notch 18650 cells like the LG HE 2, or the latest sanyo ncr 18650 ga.
What if I make "half a pack" to start with? 20s7p? Then I can build a matching pack later on when money is not as tight or our NOK currency have bounced back?
What can I expect of "drive time" for such a pack?@20 mph, @35 mph and @WOT? Will the LG HE2's high C rate be enough to pump plenty of current and phase current to the fat hub?

Argh. My brain is having a meltdown. I feel like a noob again. Spot welding my own pack is far outside my comfort zone, I will that you that much. :?

 

[Allex]

I would not recommend LG they have to optimistic data sheets and don't live up to them.
LG HE2 is old school, better go with Sammy 25r or even Sammy 30Q that I have been building with lately.
Use GA cells when you need lots of range at modest power levels. The above ones if you are looking for performance.
7p is enough when using performance cells if you can live with a volt sag of about 8-10V at say 140Amps.

Drive time hard to calculate, you first need some kind of values to lean on with your old bike, before we can start calculate. But I will give you a hint I consume 25Wh/km on average where the speed is between 20 and 100km/h (short bursts) on a 10kW bike and 50Wh/km when I am having fun on the trails

WOT is easy, about 2 minutes before QS motor starts the melt down

 

[Ohbse]

Ohbse - you may not mean what you’re saying in a derogatory way but that’s exactly how it comes across, IMO.

Agreed, reading back that post did come across poorly, I won't go back and re-write but will work on my tone

Great analysis by Allex. 18650's are a pretty rapidly evolving field, new models come out quite regularly. There are three important metrics you need to consider when selecting a cell, this applies equally to Lipo as it does to can cells:

Price - of course! This can be broken down in a number of ways, however as Allex touched on the best way to evaluate is on a wh/$ basis. Larger capacity cells (in the same volume) may be more expensive, however you may require less of them.

Power - another way this can be thought of is internal resistance. Higher iR means less power delivered, more heat. The equivilent in Lipo is the advertised C rates. You can actually reverse engineer the HK 'rated' C rates to obtain an approximate cell level iR which you can extrapolate to forecast pack performance.

Capacity - this is how much energy the cell contains. More is better, but there is a compromise to be made - generally as capacity increases, internal resistance also increases. This is why 'power' cells generally aren't right up at the 3500mah level but 3,000mah or less. This comes down to cell chemistry and is a complex topic unto itself. With time has come cells that have both MORE capacity and LOWER iR. These are just plain better. A recent example is the Samsung 30q cell with 3,000mah - these actually have exactly the same or even slightly lower iR as the older Samsung 25r cells with 2,500mah. However of course this is reflected in the price :lol:

Remember that old adage, Fast, Cheap, Good - pick two? This pretty much applies to battery packs too with the above metrics. There are additional concerns around maintenance, reliability, lifespan etc but will try to keep this relatively simple.

Here's a couple of examples from HK appropriately enough

Turnigy nano-tech A-SPEC G2 4250mah 4S 65~130C Lipo Pack
138x45x36mm = 223.56 cm2 volume
4250mah = 62.9wh = 281wh/litre
455g = 138wh/kg
$82.92 = 0.76wh/$
Power output = 4089w = 8987w/kg

Multistar High Capacity 4S 10000mAh Multi-Rotor Lipo Pack
160 x 65 x 36mm = 374.4 cm2 volume
10,000mah = 148wh = 395wh/litre
804g = 184wh/kg
$58.39 = 2.53wh/$
Power output = 1480w = 1841w/kg

As you can see, each of these examples has quite dramatically different stats! The Multistars emphasize capacity over power at an affordable, but not bargain price. The Nano-tech prioritise power over everything. There is a similar spectrum of choices in the 18650 market. 18650's in general are closer to the multistar end of the spectrum, peak power delivery is not their sole focus however as Allex's breakdown highlights they exceed lipo in not only price but also capacity, be it by weight or by volume. There are other advantages in that they're tested to destruction and certified not to burst into flame by the manufacturer, they're inherently more stable being in a metal can and while cylinders are not volumetrically efficient they can be packaged into weirder shapes being individually small potentially resulting in more juice in your available space.

 

[Hillhater]

Careful guys, you are not comparing apples etc.
You are comparing a single cell 18650 with a multi cell lipo pack fully connected and ready to run.
Run the figures again and try using the more commonly used 6s, 5.0 Ahr, 20C HK lipo ($40, 765 gms)
And also compare finished "pack" costs for say a 48v, 10Ahr or 20Ahr pack fully assembled, wired , ready to plug and go !
....and try to use an 18650 with a rating that would allow a 50 A continuous pack discharge !

 

[ElectricGod]

I had forgotten that lion cells have a higher charge density than lipo. Can someone recommend where to buy the Q30's or equivalent for a reasonable price? I have looked around, but seen most 3000mah 18650's going for close to $6.50 per cell. That gets awfully expensive super fast. I considered buying cheap laptop batteries and harvest the cells, but they tend to have 2600mah cells in them and the C rate is pretty low too. Crack one open and there's Chinese cells in them, made by who knows what company. If I am going to invest in lion, the price needs to get down in the $3 per cell range....or lower. Since lions commonly come in 3000mah, that about where I would likely go for cells. More capacity gets you a tiny bump for a lot more cost as far as I can tell.

There's got to be a way to get decent 18650's without spending a fortune for them. Truthfully 25C is plenty for me. I don't need insane discharge rates, just lots of capacity without spending a fortune. Getting a spot welder and nickle strips is a small concern compared to $1000 worth of cells.

 

[Ohbse]

Hm how cheap can I be and still get fast acceleration from the QS 205 hub? I will need to spend cash also on spot welder, car battery, nickel strips, etc.

My plan was 20s14p. But do to weak currency at the moment this will be too expensive if I choose top notch 18650 cells like the LG HE 2, or the latest sanyo ncr 18650 ga.
What if I make "half a pack" to start with? 20s7p? Then I can build a matching pack later on when money is not as tight or our NOK currency have bounced back?
What can I expect of "drive time" for such a pack?@20 mph, @35 mph and @WOT? Will the LG HE2's high C rate be enough to pump plenty of current and phase current to the fat hub?

My previous post is background info for your question. To choose a cell (and then determine how many cells) you need to define your requirements. Allex's estimates are bang on with my experiences with fast commuting on a big hub street bike, ~25wh/km is a good figure to work with. With that in mind - how far do you want to go in a stint?

In my case I needed the ability to go 50km @ 30wh/km = 1500wh. This was a bit of a worst case scenario where I'm going fast the whole time and had to add an errand or detour to usual daily ride. You don't want to size a pack to be completely drained, good rule of thumb I work to is oversize by 20%. 1500/.8=1,875wh required. Calculating the wh capacity of a cell is as simple as the rated nominal voltage x capacity in Ah. In my case I purchased LG HE4 cells which are 3.7v nominal and 2.5Ah = 9.25wh. 1875/9.25 = 202 cells to deliver the energy I need. I wanted to run 20s to best work with the Adaptto controller, so 202/20 gives me 10.1 which obviously needs to get rounded to a whole cell. Physical constraints in my battery box meant that 11p was not feasible, so 20s10p it is.

The nominal cell level iR on the LG HE4 is ~25mOhm. This scales out to deliver a pack level iR of about 50mOhm. This is a dynamic figure and varies with temperature, state of charge, age of cells etc but it's not a bad number for estimation. This pack iR means we can simulate the pack performance in a number of different situations. Full power at rated current (200 amps) we can determine that this pack will deliver:

14.8kw power output
2kw of heat
Sag of 10v

At a more realistic drain of 85a:
6780w
360w of heat
Sag of 4.25

That's acceptable power performance, enough capacity and the price was equivalent to lipo but with plenty of other advantages, 200wh/kg energy density etc. I have since done 280 cycles of varying depth and capacity loss is about 3%. HK Lipo would not have fared so well.

I would caution against building a half sized pack if you really need the full size pack. It's far, far better to have an unstressed battery, you're going to get exponentially more life out of it. If on the other hand you're looking for performance, but only for 10 minutes at a time.. perhaps a cell at the power end of the spectrum is more appropriate.

 

[ElectricGod]

What about 32650 cells? I have seen 5000 to 6000 mah cells. I found these on alibaba. I have no idea what the C rate is or how good they are. Are larger lion cells better than smaller ones? I think in regards to number of cells and number of connections, then I think fewer large cells is better than lots of smaller cells. That was essentially why I have been using 8000mah lipos...lots of capacity without lots of complications with hundreds of connections. I'm asking about them, but haven't heard back yet.

http://www.alibaba.com/product-detail/6000mAh-cylindrical-Lithium-ion-battery-32650_60091156193.html?spm=a2700.7724838.30.104.oa0OSS

 

[Ohbse]

Careful guys, you are not comparing apples etc.
You are comparing a single cell 18650 with a multi cell lipo pack fully connected and ready to run.
Run the figures again and try using the more commonly used 6s, 5.0 Ahr, 20C HK lipo ($40, 765 gms)
And also compare finished "pack" costs for say a 48v, 10Ahr or 20Ahr pack fully assembled, wired , ready to plug and go !
....and try to use an 18650 with a rating that would allow a 50 A continuous pack discharge !

Last post I expanded the scope a little to the pack level. Lets do another example using your defined requirements

'48v' packs actually seem to vary a little in terms of cell count depending on who you're talking to. This is really a vestige of the days of lead acid. For ease of calculation I'm going to go with a 12s configuration so I can use the 6s pack you mentioned.

8 of the 6s/5ah packs will give us our 12s20ah pack. Each of these packs deliver 108wh for a total of 864wh. The lipo pack will be 6.2kg including the required harness to parallel pairs of packs and then connect in series. Total cost including harness ~$340.

To equate this using Samsung 30q cells we will require 7 parallel cells for a total of 84 cells and 907wh. Including spot welded nickel, shrink wrap, kapton tape, nylon sheet, foam and some 10ga wires to terminate to connectors this equates to bang on 4.1kg. These cells are available in small quantities from reputable retailers for ~$5ea, from chinese distributors in large-ish (>100 cells) for around $3.80 last time I looked. Including other consumables I would estimate pack costs of between $340 and $445.

Using the upper estimate the wh/$ works out to be 2.54wh/$ for Lipo VS 2.04wh/$ - 2.67wh/$ depending on your final cell costs. Of course there's a pretty substantial weight saving, not to mention the volume difference. To some people that's worth plenty, as the bulkier pack simply won't fit where they need it to. For other applications not so critical.

Another comparison between these two options is to compare kwh delivered over their lifespan. As a rule I would expect 250 80% cycles from the lipo pack and 500+ from the 18650's, assuming no early failures etc etc. That's based on real world as well as some synthetic testing. The Lipo pack delivers 172kwh VS 362kwh for the 18650's. This is of course a gross over simplification and frankly it's probably too kind to the lipo based on failure rates, but it gives you another point of comparison that really makes a difference if you use these things frequently.

Both packs will comfortably deliver 50a continuous efficiently.

 

[Ohbse]

What about 32650 cells? I have seen 5000 to 6000 mah cells. I found these on alibaba. I have no idea what the C rate is or how good they are. Are larger lion cells better than smaller ones? I think in regards to number of cells and number of connections, then I think fewer large cells is better than lots of smaller cells. That was essentially why I have been using 8000mah lipos...lots of capacity without lots of complications with hundreds of connections. I'm asking about them, but haven't heard back yet.

http://www.alibaba.com/product-detail/6000mAh-cylindrical-Lithium-ion-battery-32650_60091156193.html?spm=a2700.7724838.30.104.oa0OSS

These are trash. Very far towards the cheap/capacity end of the spectrum. They are ~3x the weight of a 30q cell, but deliver only 2x capacity. They're also rated for 'fast discharge' at 1c or 6a, so power density is very bad.

Logically speaking, fewer large cells is indeed superior. Simplicity is supreme. In reality the products available are simply dramatically better in the specific 18650 format because of the wide scale demand for powerful and reliable cells out of the power tool industry and now from the large format EV market thanks to Tesla. This more than justifies the increased effort in assembly.

Prismatic pouches are more volume efficient, however they're also incredibly delicate, they also suffer from scalability issues as the size of the pouch increases. Recycling large format cells from commercial EV's like Nissan Leaf cans and modules from Volt etc is a great way to go but subject to availability problems.

 

[nutnspecial]

Good info, lighter pack for same money (less assembly and tools). Better cycles. Safer.

I would give the 20c 20ah lipo a conservative real world 100a constant discharge. (25% c)
I have the suspicion the 20ah referenced cans will be lucky to achieve 50a constant?

So what is the c rate of the cans you are comparing?

 

[ElectricGod]

ohbse...thanks for the input. Options are what I am looking for that are reliable and worthwhile.

Does anyone have any experience with the chevy volt type cells? They are effectively giant lion cell phone batteries. It seems like they are easy to implement and take care of since they are lion batteries. Looking on ebay, there are several people selling new and used ones. I think availability is reasonable and if they are good enough for a commercially made care, then they are probably good enough for us EV experimentors.

 

[ElectricGod]

Good info, lighter pack for same money (less assembly and tools). Better cycles. Safer.

I would give the 20c 20ah lipo a conservative real world 100a constant discharge. (25% c)
I have the suspicion the 20ah referenced cans will be lucky to achieve 50a constant?

So what is the c rate of the cans you are comparing?

I just emailed the seller so I don't know anything more about them than what I just posted.

 

[nutnspecial]

Does anyone have any experience with the chevy volt type cells?

Seems to me 'dnmun' might be the 'God' of those around here. . . :wink:

 

[ElectricGod]

Does anyone have any experience with the chevy volt type cells?

Seems to me 'dnmun' might be the 'God' of those around here. . . :wink:

LOL! Glad people are having fun with my ES moniker.

 

[Ohbse]

Good info, lighter pack for same money (less assembly and tools). Better cycles. Safer.

I would give the 20c 20ah lipo a conservative real world 100a constant discharge. (25% c)
I have the suspicion the 20ah referenced cans will be lucky to achieve 50a constant?

So what is the c rate of the cans you are comparing?

HK Lipo is rated effectively to sag to nominal voltage from HOC 4.2v. That's hitting the cells very hard indeed. Hence the reality check C rating of 1/4, this gets you back to something a little healthier.

18650's are more sensibly rated by the manufacturer and you can usually find discharge info. The Samsung 30q cells are rated at a continuous 15a or 5c. The LG HE4 cells I used are rated at a continuous discharge of 20a or 8c. In the case of a 7p pack drawing 50a you're going to be hitting each cell at ~2.4c or 7.1a. About half their rating. 2.5v of sag delivering 2.4kw of output.

Personally rather than go with the much lighter 18650 pack I would build an 10p pack, still a little lighter but now 50a discharges would barely tickle it. Drop HOC voltage to 4.05 and use a smaller percentage of total capacity, dramatically increasing lifespan yet again. More money up front, but a better solution long term. Plus you could always turn up the wick if 50a got boring

Volt stuff is good, but once again run the numbers - they're at the power end of the triangle - energy density is about the same as mid tier HK lipo. Quality is going to be better, lifespan definitely better - but if you're buying second hand modules then somebody has already used up a chunk of that. Packaging is difficult, you can't easily get down to individual cells without causing substantial but hidden internal damage as they're glued together. If you can break down the OEM modules and retain the structure in your application then they're a great option.

 

[ElectricGod]

Good info, lighter pack for same money (less assembly and tools). Better cycles. Safer.

I would give the 20c 20ah lipo a conservative real world 100a constant discharge. (25% c)
I have the suspicion the 20ah referenced cans will be lucky to achieve 50a constant?

So what is the c rate of the cans you are comparing?

HK Lipo is rated effectively to sag to nominal voltage from HOC 4.2v. That's hitting the cells very hard indeed. Hence the reality check C rating of 1/4, this gets you back to something a little healthier.

18650's are more sensibly rated by the manufacturer and you can usually find discharge info. The Samsung 30q cells are rated at a continuous 15a or 5c. The LG HE4 cells I used are rated at a continuous discharge of 20a or 8c. In the case of a 7p pack drawing 50a you're going to be hitting each cell at ~2.4c or 7.1a. About half their rating. 2.5v of sag delivering 2.4kw of output.

Personally rather than go with the much lighter 18650 pack I would build an 10p pack, still a little lighter but now 50a discharges would barely tickle it. Drop HOC voltage to 4.05 and use a smaller percentage of total capacity, dramatically increasing lifespan yet again. More money up front, but a better solution long term. Plus you could always turn up the wick if 50a got boring

Volt stuff is good, but once again run the numbers - they're at the power end of the triangle - energy density is about the same as mid tier HK lipo. Quality is going to be better, lifespan definitely better - but if you're buying second hand modules then somebody has already used up a chunk of that. Packaging is difficult, you can't easily get down to individual cells without causing substantial but hidden internal damage as they're glued together. If you can break down the OEM modules and retain the structure in your application then they're a great option.

I have space for a mondo pack if I want to add one so volt batteries are an option I can pursue easily. Also, buying new volt batteries are not much more than used ones. Hopefully I can get 2 or 3 years of daily use out of them. At 47Ah and running at maybe 3C, I probably wont tax them much. I can buy brand new 2015 cells which have a little more capacity than the 2014 cells.

The other option is 18650's which I am OK with and building up a custom fitted pack. I'm sure with lots of small cells I can fill this space better than it is currently filled. It would look a little odd, but a monolithic T-shaped slab of cells would be an efficient use of the space. I just need to know where to get them for a reasonable price.

 

[Ohbse]

I have purchased from and have had others also order with good success from "Shenzhen E-fire Technology Development Co.,LTD" http://www.cl-rd.cn/

Friendly, flexible, good pricing. I would recommend asking for pricing from a couple of different reputable Alibaba suppliers. Key to success with ordering cells from China is the supplier getting the packaging right, if you get a quote for shipping dramatically lower than competitors I would be asking why. I've heard all sorts of horror stories of batteries being seized by customs due to deliberate mislabeling etc. Ms Little Bear (that's really her name) from Shenzhen E-fire was excellent and all the cells I have ordered were packaged individually and to the letter of the law regarding lithium shipping.