Homemade Battery Packs

Index - January 2022 Updating

Tools and Parts

LiPo vs SLA

18650 info
18650 cell specs by manufacturer
18650 chemistry by model designation

Recent

12.8V 1.280kWh portable power w/inverter
FIRE - not Lithium!
Resurrecting "dead" ( extreme low voltage Lithium cells ? )
Max Life and performance by mapping
Miles per kWh
Ni-Cd Rejuvenation
Update on recent battery builds
Performance variance from Batteries with lower usable voltage
LiPo Resurrection?
Geteed 26650
Mapping Cell Placement
Cell Testing Methodology
1st LiFe cells (Fullriver 26650's)
33.3V 31.2Ah (9s12p) 1kWh+ - 2018
25.9V 26.4Ah (7s12p) Samsung ICR18650-22p (New Cells) #1 - 2017
25.9V 26.4Ah (7s12p) Samsung ICR18650-22p (New Cells) #2 - 2017
Battery Day (2017)

Recycled laptop Lipo
The beginning
Quick Testing LiPo 6 Packs
Optimal voltage Range I
Optimal voltage Range II
33.3V 43.2Ah Lipo Build
2014 Laptop (new) LiPo Build - 25.9V 25.92Ah
2015 Laptop (new) LiPo Build - 25.9V 25.92Ah - positioning in eZip Pack
Dell Laptop LiPo Capacity Map
LiPo Overload - Massive Batch Testing
1000 LiPo Cell Batch
SONY LiPo Mapped
SONY LiPo vs Unbranded LiPo - from Dell 2nd bay packs

BBB Bargain Battery Buys!
10s4p 36V 14Ah MJ1 eBike batteries @ $60 each
12s2p LG 30A cells
Just lucked into new 14s (51.1V) 4p (6Ah) LG HB2 120A continuous output modules - 6lb.
Got 6 @ $39.99 each ~ $130 per kWh

Recycled laptop 18650s
The basics
2008 builds
Finding Laptop packs for Recycling
Opening packs
Bleed Down - Voltage "Leakage" Test
Bleed down - self discharge test necessary?
To BMS or not?
BMS or not - 2011
Recycled Packs For Sale?
Once Again!
29.6V 31.2Ah eZip Pack = .932kWh Pack!
Age Deterioration?
Winter 2013-14 33.3V 31.2Ah 18650 Build - in eZip pack!
Serial - Parallel Schematic
2015 "New" 33.3V x 31.2Ah = 1038.96Wh (1kWh+) - eZip
18650 Wiring Diagram
Sanyo discharge graph
Sanyo Cell Discharge Characteristics
18650 prefixes and suffixes

Soldering
Soldering 2013
Soldering 2013

Testing Recycled Cells -
Cell Testing Methodology - 2018
2011 Method
2013 Method
2013+ Method
2014 Method
2015 Method
Dedicated Thread - Bulk Capacity Testing
Check list for bulk testing
Copper tape covered magnets

RC Lipo
RC Lipo Day

LiFePO4
1st LiFe cells (Fullriver 26650's)

BMS - PCB - ?
To BMS or Not to BMS - 2015

Bulk Charging - Testing Cells
Cell charging - Testing - Selection
Bulk Charging Review
MeanWell Mega-Mods
Paralleling a regulated PS with an unregulated PS
Test For Bulk Charge Feasibility

eZip RMB - Battery Pack Rebuilds
25.9V 25.9Ah (7s12p) LiPo - 2011
25.9V 31.2Ah (7s12p) Li-ion - 2011
29.6V 31.2Ah (8s12p) Li-ion - 2013
33.3V 31.2Ah (9s12p) Li-ion - 2013
22.2V 41.6Ah (6s16p) Li-ion - 2013
22.2V 30.24Ah (6s14p) - 2014
25.9V 25.9Ah (7s12p) LiPo (New Cells) - 2014
25.9V 26.4Ah (7s12p) Samsung ICR18650-22p (New Cells) #1 - 2017
25.9V 26.4Ah (7s12p) Samsung ICR18650-22p (New Cells) #2 - 2017
33.3V 31.2Ah (9s12p) 1kWh+ - 2018

eZip RMB Battery Pack
eZip RMB Pack - Pros/Cons
OEM voltage w/16T mod ~20mph vs 33.3V w/oem gearing ~20mph

And Sadly ...
Self Discharge vs The Illiterates - ebeach & dnmun being "stubbornly ignorant" for ~50 postings - Belligerently against something they misread(?) ... over and over - again and again!

Capacity Testing
Basic-Simple Method
2011 method
Low Tech Capacity Mapping - Finding Optimal HVC & LVC
Capacity Testing - Quick Method
3 Methods
Comparative IR as Capacity Estimate

Determining Optimal DOD and Charge Voltage
Max Life and performance by mapping
Capacity Mapping
Capacity Map - PowerStream
Optimal Charge Voltage
Reduce Charge-Float Voltage to Double+ Pack Usable Life
3.6V vs 3.7V?
LiCo Capacity Map - Alternate Source
RC LiPo WinForce 5700mAh Capacity Map
Dell Recycled Laptop LiPo 2004-06-08-10 Capacity Maps
Capacity Maps For Optimal Capacity-Lifespan

Cell Arrangement
Mapping Cell Placement
Power Rail Connection Points]Power Rail Connection Points


How safe are 18650 cells?
"Explosion" - "Fireball" tests! ala LFP
Manufacturers Safety Testing

Discharge Rates
18650 cell test
Discharge Depth?

C Rate
C Rate?
C Rate as a Function of Actual Capacity
C Rate Damage
Re: C Rate Damage

Internal Resistance
Comparative IR - Internal Resistance
Using Internal Resistance to Estimate Capacity?
Comparative IR (Internal Resistance) as Capacity Gauge

Battery Deterioration
Battery Deterioration

Toolbox
Cheap 18650 dual chargers
iMax B6
Balance Plugs
3s Balance tool
Budget 25.9V 7s Li-ion charger
1s-8s Low voltage meter-alarm < $3
Voltage Ah watt 20 amp meter
AC Power Cords?
6s Charger > 12s Controller Full Switch - or Double Voltage for Turbo!

Battery Build Roundup - Pictures

2011 Builds
Plans
25.9V 31.2Ah in eZip pack
25.9V 26Ah Recycled Lipo build
2011 18650 build - 1 Year report
2011 Lipo build - 1 Year report
2011 Lipo build - 2 Year report

Charging
Bulk Charging
Modded Meanwell
Bulk Charging Testing
Regulated and unregulated PSs in Parallel

Balance Charging
Using a large capacity bulk charger in conjunction with a balance charger

Fuses
32V - 58V - 80V - 125V Fuses

Connectors
Deans Plugs
More ...

Wire Gauge
[urlhttps://endless-sphere.com/forums/viewtopic.php?f=14&t=26383&start=875#p883923]Wire gauge Amps?[/url]

Pre-Charge Resistor
Pre-charge Switch

Troubleshooting Pack
Finding Weak Cell-Cells

More Plans
RC Lipo in eZip pack
2008 Nimh test
44.4 MAGNUM
Li-ion vs SLA
LiPo vs SLA -2016
2008 Rebuilds
22.2V?
33.3V Builds
Legal 20mph w/30mph TURBO Mode

Related Threads
Bulk Capacity Testing
Determining Capacity Profile - 3 Methods
eBike Toolbox - Bargains
Efficiency?

Other Li-ion uses
Power tool rebuilds

Torque-efficiency via throttle position

22.2V-24V-25.9V Torque - Speed profiles

Capacity "Mapping"

Wire Gauges?

Spot Welder idea-plan

Cordless Power Tool Lithiumizations

Cordless Power Tool Battery Upgrades-Conversions

Electric Lawnmower Battery Builds
Electric Lawnmower Battery Upgrade
7s RC LiPo
B&D Firestorm Upgrades

More DrkAngel Threads

20mph or Bust(ed) - USA "Legal" eBike Speed
25 eCars - Pics And Specs
44 Magnum!
Aerodynamic Factors
Battery vs Cold
Bicycle Safety - The Math of Speed
Broken Spokes - eZip - Solutions!
Bulk Capacity Testing
Cheap Chargers - Trimming Voltage
Creature Hazards!
Currie-iZip eBike Kit - Amazon.com
Determining Optimal Charge Voltage
Dual Voltage Rig
eaBike vs eBike vs eMotorcycle
eBike ToolBox - Bargains
eBike As Cyclist (Health) Assist
eBike Battery Heater
eCar Hybridization
eCars - Compared
eTrike Conversion - As Mobility Device
Electric Assist vs Pedal Assist
eZip Trailz - On Sale $
Forming Custom Battery Cases
Grim News On the Oil Front
Haro Express Deluxe Build
Lead Acid Woes - Sulfation etc.
MeanWell Mods - S-150-24
MeanWell Mods - S-350-48
Most Annoying! ...
Motor Output Watts Required For MPH?
Multi-Voltage Testbed - eZip
Peak HP - Controller Have Enough Amps?
Prolonging the Misery!
Rolling Resistance (RR) - Understanding Tires
Simple Hybrid eTrike-eBike
Speed vs Range
Studded Tires!
Sprocket Ratio = Pedal Assist Speed
Voltage Rebound - LiCo
W.O.T. Addiction - Withdrawal
Watts = MPH (eMotorcycle)
Winterized

eZip - iZip Specific Threads

eZip Trailz Commuter - 2014½
EZip Trailz LS - 2013
Re-volting the eZips ... Simple Mods!
The New EZip "StepThrough"
Currie-EZip ebike Kit $289.88 - Amazon.com
eZip-iZip-Currie parts-n-such
13T Drive Sprocket - Currie, eZip, iZip
Re-gearing the eZips - Simple Mods!
EZip Trailz - On Sale!
Multi-Voltage Testbed - eZip
eZip-iZip Usable Controller Voltages
Should I lube my izip motor?
EZip - IZip 20mph Upgrade $20!
eZips - 15T drive sprocket
Currie-eZip-iZip Mods & Such - 5 Year Journey
Currie - IZip eBike Kit - Price Tracking
EZip Trailz - Continuous Price Tracking
Broken Spokes - EZip - Solutions!
14ga to 12ga Spoke Upgrade
EZip Basics ... Electric Bike or Electric Assist Bike
Currie MY1080Z 450w Motor - capabilities (EZip-IZip)
11T Mod - 20mph (25.9V)
EZip Trailz LS - 2013
eZip Turbo

Please take note!
Methods and procedures are continually being developed-improved,
Use Index! - Available in signature of every DrkAngel post.

Prologue - I started with an EZip Trailz 24v SLA pack.

Being sadly disappointed with the performance ...

I soon Upgraded to 36v SLA.
Was disappointed with range and weight, so ...

Tried a 24v - 20 cell pack of 7ah D cell Nimh, seemed inadequate so I added another 20 cell bank.
About $140 for the 40 cells and $40 for the charger.

Thought I could do better so ...

Recycled "bad" notebook batteries into long range Li-ion batteries.

25lb 36v 10ah SLA - unassisted range@16mph = 12 miles
Replaced with:
9lb 37v 20.8ah Li-ion - unassisted range@16mph = 30 miles+

"Bad" battery cost - about $30 + $80 for PCB & charger.
Plus work, of course, testing, soldering etc.

37v not compatible with newer models so I built 25.9v versions.
9lb 25.9v 31.2ah Li-ion - unassisted range@16mph = 40 miles+
Cost? About the same as the 37v Li-ion.

Li-ion notebook battery pack are nice because they have nice solder tabs.
Cheap too, 90%+ good, out of "bad" packs.

Downside? Surge output - about 1.5C, sustainable ... <1C.
Not bad since I cruise at 20mph, but not sustainable at 30mph, with my 9lb battery.

Now I'm building 3 new prototypes:

#1. Lithium Polymer from recycled notebook batteries.
Just bought 120 2.16ah cells for $40 - can use my Li-ion components.
48v 20ah pack, or -
37v 25.92ah pack, or -
25.9v 37ah pack.
Weight? About 12lb. Not sure about C rating yet, probably 2C+ sustainable.

Will test, peak C, sustainable C, built in fuse activation point.
And will post results.


#2. New RC Lipo 10 - 11.1v 5700mah packs.
20C surge 15C sustainable.
30 3.7v 5.7ah cells
Total cost ? About $200.
48v 11.4ah pack.
37v 17.1ah pack
25.9v 22.8ah pack
Charger and PCB - about $100 - $120, can use my Li-ion components.

#3 LiFe from recycled battery packs.
80 - 3.2v 5ah cells,.
Cost? about $160.
25.6v 50ah pack
38.4v 30ah pack
48v 25ah pack
Charger and BMS not priced yet, but should be near $150.

All cells acquired, am presently charging-testing individual Lipo cells.
Will do preliminary tests with a 22.2V, (25.2v at full charge), 21.6ah pack, on a 24v bike, (batteries are arranged in 3 cell, (11.1v), "bricks").

After individual charging, bricks will be precisely discharged, any voltage variance between cells, should pinpoint anything, weak, damaged, or substandard, and will be eliminated before "pack" assembly.



Will post pictures and progress reports

Interesting project. I'll be following this thread.

DrkAngel said:

#1. Lithium Polymer from recycled notebook batteries.
Just bought 120 2.16ah cells for $40 - can use my Li-ion components.

Click to expand...

That's 4.3 cents/Wh!!! Sounds like a real bargain assuming that the remaining cells' capacity are at least 50% of the original ones. How old are these cells and where did you buy them from? I didn't know that you can buy recycled notebook batteries.

Got my 20 - 6 packs of Lipo. 1 mated pair of cells was bad.
Still that is $40 for nearly, a 1KWH battery pack!(.96KWH)

Took 1 - 11.1v - 4.32ah brick, charged it to the nominal 12.6v, hooked it, with an amp meter, to a 12v 250w leaf blower, it surged to 20 amps, then settled to 11 amps, as leaf blower attained speed.
About 15 seconds later, one of the built-in fuses, blew.

Fuse is easy to bypass, but my 25.9v pack will have 6 banks of these bricks, or about 120amp surge & 60+amps continuous capability!
Present bike's, noticed, surge usage was barely 30 amps, continuous is about 15.

And! ...
I scraped the scummy SLAs out of an EZip pack, and was able to stack in almost 26ah of Lipo! (25.92ah)
Or ... could fit 17.28ah @ 37v.
A little better than the 24v 6ah usable, provided by the OEM SLAs!

Weather is lousy, so I'm charging - testing -discharging - more testing, to confirm, best cells, before assembly.
Will keep everyone posted!

Recycled Lipo! (Lithium-ion Polymer)

Lipo cells are ready!

Bricks of 6 6packs of dbl cells.

Each Brick:
contains 72 individual cells, at 2160mah.
measures 2-3/8" x 4-7/8" x 4-1/2"

37v 25.92ah pack is almost 9" x 4-7/8" x 4- 1/2" and weighs under 12lb
Uses 3 Bricks & (2 6packs, re-wired for a combined 3.7v)
Now I need to find a sturdy, weather resistant, container.

25.9v 25.92ah pack fits snugly into EZip case, about 9lb
uses 2 Bricks & 6 separated dbl cells, run in parallel, for 3.7v
3.7v cells must be placed sideways at end of bricks, leaves nice room for wiring.

5 Bricks produced, plus all the 3.7v for both packs

Still waiting on bleed down test on 3.7v cells, and connectors for EZip pack
Should have everything Monday and, 25.9v assembled
Will be hunting for 37v package, box ... 6pack cooler is just not long enough!

EZip pack will be assembled with a 7s balancing connector on the batteries. Charging will be accomplished with an iMax B8. Initial charging will be done by opening case and to take advantage of balancing capability, and thermal probe. Eventually, after monitoring several unregulated charges, I may charge solely through the normal charge port. With the occasional disassembly and "balance" charge, to insure optimal voltage equalization.

Alternatively, I will cut a small "window" for access to balance & thermal probe connectors, and seal with, tape etc.? I would like to maintain a weather resistant construction.

Pictures & performance - range results ... coming soon.
Waiting on some decent weather.
Still too wet and cold for prolonged bikin'.

Looks like a lot of fun. How do you test the cells? I'm interested in doing this just for fun.

2 of your 3 projects involve lipo.
I knew you wouldn't stay with the dog meat 18650 cells for long.

That being said i'll leave the rest of my opinions at the door and let the lipo do the talking from here ;]

I just 10 dell 56wh laptop batteries go for $100 shipped on ebay. That's 560wh for $100. Even if half the cells works it's still twice as good as 20c lipo. It would make good batteries for 36v "girlfriend" kits.

Love it I'm starting to go dumpser driving. Not just like it sounds but will take a page from Amberwolf and use the useable or unwanted. Sorry got to go and and check off a dumpster.

auraslip said:

I just 10 dell 56wh laptop batteries go for $100 shipped on ebay. That's 560wh for $100. Even if half the cells works it's still twice as good as 20c lipo. It would make good batteries for 36v "girlfriend" kits.

Click to expand...

What a coincidence auraslip. I too bought 20 Dell 56wh batteries for $120 ($6/each) locally. I have so far used only 16 of them to make my 12s 10Ah pack. May be I was lucky, at least 4 of 6 cells in each pack are good. At 0.5C draw they provide 2.5Ah. 2.2Ah at 1.0C draw. The cells are completely cool at 0.5 and 1.0C draw. At 2.0C they get warm (not hot) and only give 1.9Ah. I love those pink cells. I going to buy another 20 as soon as they are available.

auraslip said:

Looks like a lot of fun. How do you test the cells? I'm interested in doing this just for fun.

Click to expand...

Check Index for newer improved testing methods

I begin by testing cells.
Cells above 3v have great potential.
Below 3v might be OK.
Even the cells that register as dead, might be resurrected.
This is because Lipo & Li-ion have built in safeties.

Resurrection:
Most Li-ion chargers will not charge these "dead" cells.
The solution is to pair the dead cell to a good cell.
The simplest method is to buy the cheapest dual 18650 charger. These chargers do not charge the cells independently. Just leave one good cell and place a dead cell as its partner. Test voltage on cell after 1 minute, if cell retains some charge, then continue charging. (Watch for cells getting hot, seldom but it can happen - place strong paper strip, or string, under bad cell, to allow puling hot cell out)
Cheap Li-ion dual 18650 Charger
Get multiple, you'll probably be working with quantities of cells, charging takes time and these chargers are less than $5 each - delivered!

These chargers also work nicely with cells pulled from notebook batteries, which are typically paired, placing half a pair in a charger works just fine, 2 for the charger of one, of course, takes twice as long.

Testing:
Charge cells to "full" 4.2v. If will not charge to 4.2v, place aside.
Let cells set 1 day, test for voltage drop, if significant, set aside.
Most important is that you find consistency among the cells.
Among same model cells, establish "normal", variance from normal is the eliminating factor.
Finally, take charged cells, individually apply a timed identical "load", recheck voltage to eliminate cells with surface charge or reduced capacity.

Cells of same capability - capacity is the object of your search.

After you have enough, build your pack.

Remember Li-ion typically do best at 1C output, or less. Of course, if you get enough cells for a 30ah pack, you might have a 40 mile range! Also, 30ah Li-ion weighs less than 16ah LiFePO4 or 8ah SLA.

DrkAngel that was great. You're half way to writing a FAQ for the technical section about building a pack with these!

I'm super excited about doing this now. Throw in a 12s bms and small charger and I got a great pack for my girlfriends bike. The largest concern with cylindrical packs is the build quality and matched cells, but by doing it yourself you can be sure it'll turn out great!

Remember Li-ion typically do best at 1C output, or less. Of course, if you get enough cells for a 30ah pack, you might have a 40 mile range! Also, 30ah Li-ion weighs less than 16ah LiFePO4 or 8ah SLA.

Click to expand...

At a $100 for per kw, it'd be easy to build a super big pack capable of huge current!



A 12s 8p pack if the cells cost $1.6 each.
18650 43.2 volts 20 Ah 9.843119999999999 lbs $153.60 864 Whs 30 continuous amps @ 1.5C

18650's recycled from notebook batteries are extremely cost effective. I've built 5 packs, 2 - 25.9v @ 31.2ah and 3 - 37v @ 20.8ah and put thousands of miles on each, well ... close to 10,000 miles, over the past 3 years.

Finding matched cells, in sufficient quantity is the worst problem. I hunt on ebay for "lots" of notebook batteries, and have standing requests at 2 local recycling plants. Not buying any notebook batteries at present, so you won't be bidding against me. I've got 5 KWH of 18650, 4kwh of Lipo, and 3kwh of LiFe, ready for testing & assembly.

Compared to the SLAs that came with my EZip, they have 5 times the usable output, at about 1/2 the weight!
And ... my cost for the Li-ion cells was less than the cost of the wimpy EZip replacement pack!
Charger & PCB were additional, however. Major limitation is that they are happiest at a 1C output, or less, so larger packs are recommended, 20ah minimum, 30ah+ recommended!

Don't be too dismayed by the "1C"!
A 40ah Li-ion pack is about the same size & weight as a 20ah LiFePO4 pack.
But, possibly, 1/5th to 1/10th the cost!

I've been collecting "bad" laptop packs for free for more than a year here in San Diego. I periodically call stores that service laptops and resell used laptops to see what quantities they've collected for eventual delivery to a recycler. Several stores seem happy to let me come by to pick them up.

Harvesting is time consuming. I monitor discharge curves on each cell, enter mAh of delivered constant current discharge to 3.7V, 3.6V, 3.5V, 3.4V, 3.3V, 3.2V, 3.1V, and 3.0V. on a spreadsheet. This is how I match cells.

I also record voltage off the charger which can be anywhere from 4.0V to 4.28 V when using a charger with cc / cv cycles. The $5 chargers are almost always cc only. The cutoff voltage on these cc only chargers vary widely from 4.05V to 4.15 V in my experience for those that work and can exceed 4.25 for those that severely shorten battery life. I notice much less surface charge on these cells than with NiMH. Accordingly I check the voltage at least 24 hours after the initial charge and dispose of cells that have dropped by more than 0.08 V

I've found that the following color wrapping usually apply:

Pink -- Samsung
Red -- Sanyo
Dark Blue -- Sony
Gold -- Sony
Grey -- LG
Lavender -- Panasonic (newer 2700 mAh)
Light Blue -- Sony, Panasonic (older), Samsung (older)

this sounds like fun, i have a couple of battery shops down the road from my place, know one takes in recycled batteries, do they just give them to you or what is the going rate, they get them for nothing so i assume they would let you take them for nothing. wonder how big a battery i can make for next to nothing. just need to find alot of time and learn how to put them together.
cheers adrian

Some pictures of my 37v Li-ion pack.



Tried many containers before finding an insulated lunch bag, at Walmart. (About $5)



It speaks for itself!



25.9v 31.2ah pack is nearly identical in size.

Fantastic stuff! I love the atx PSU motherboard balance cable and the main power cable.

A couple tips, concerning notebook batteries:

Opening packs - Try prying apart,
Place pack in freezer - tap with light-very small hammer, (medium size wrench, screwdriver handle etc.) along seam - usually cracks, allowing easy separation.

Tin snips open some packs nicely. Disassemble 1 pack using safer method - determine possible damage-danger points, before cutting into identical packs.

Do not separate cells - connecting tabs often make pack assembly extremely easy
Caution: metal tabs are often very sharp - gloves are a good idea.

What amp. will you run your controler at ?

999zip999 said:

What amp. will you run your controler at ?

Click to expand...

?

The controller runs at whatever amps the throttle tells it to.

I'm guessing, but I think you are asking:

Q: What amperage controller do you have?
A: Typical controllers are rated at 25 -40 amps, they might surge past that for brief periods.

Q: What amps do you run at?
A: Typical start & acceleration is near 30amps reducing to 10-15amps at cruising speed.

Q: What amp pack of Li-ion do I recommend?
A: Since my maximum demand is around 30amps, I would recommend a 30ah, or larger pack.

My motor is a 24v 450w output brush motor.
At 37v, output is near 675w.
Same max amps.
OEM SLA pack comes with 40amp fuse.

Hope I gave you an answer that satisfies you ...

I've read some people here have had trouble soldering the packs. The heat from the soldering iron causes thermal runaway or something and the cells explode!
Do you harvest the cells with the tab intact or something?
That's my main worry!

IVe manufactured over 15 48V-20AH packs now with 18650 packs from laptop battery packs ( free source, long story)......

To be honest, as long as you have
Cutting Pliers
Goid Flat Pliers
Temperature controlled soldering station ( £40 maplin.co.uk)
good 2 core solder
lots of bandaid
patience

then you can make yourself a great battery pack...its not about AH peak, its about having so much capacity spare, you never need to tax the pack

I would pay $20 for an in depth ebook and making these packs

Dirtyginge, what did you do with all these packs? Give them to friends?

Soldering 18650's.

I have soldered hundreds of cells, and have picked up a few rules for safety, reliability and ease.
Not the final "best method", but fair, basic guidelines.

If pulled from notebook packs, they are pre-tabbed, soldering is simple.

If bare cells, more difficult.

1. Make sure that solder points are clean, abrasion, with emery cloth, or dremel tool, works great. Typically, there is a "glaze" or plating present, scraping with a sharp knife works, also.
2. Use soldering paste - flux, a slight dab is plenty. (I use a Q-tip)
3. Apply small bit of solder to soldering iron, (25w minimum, higher recommended), allow to attain full temp.
4. Apply to abraded fluxed point for 3 seconds, remove iron and confirm solder bead applied. If failed, allow to cool, then reflux and retry with slightly longer application.
5. Connect cells. I just began using a pre-tinned copper braid, (Tinned Copper Braid). It works wonderfully. Pre-flux and apply small bead of solder to braid, or wire, at the connection point.
6. Apply braid to cell, apply solder to iron, pause for temp raise, push iron on top of braid till it collapses onto cell.
7. Remove iron, braid must cool for several second, before setting.
Tip: Use probe to position and hold soldered wire etc.
It is important to not have movement while solder solidifies or solder joint will be very weak!
Small cheap chrome plated screwdriver works nicely.

Method should be adjusted for variations, quality and wattage of soldering iron is the major variable.
A more powerful iron spends less contact time on battery and actually transfers less heat.

Practice can be done on "dead" cells.
"Practice makes perfect."

Thanks again drkangel - you're the man

For BMS, you should look up smartec on alibaba. The wanted $50 for a 16s 70amp continous bms shipped. I imagine a lot of that is shipping, so you could get quite a few for your different packs.

Looking at ebay, a lot of the "bad" packs seem to be from older models. I imagine they would not be a good source for cells that haven't been used much right? Should I look for "bad" batteries from newer models. I'm thinking they're "bad" because one cell failed for whatever reason, but the other cells still have a good amount of cycles in them.

I'm going to a computer recycler next week for some server power supplies for charging. I'll ask them about batteries too.

What a great thread! I'm in the process of ordering my first hub kit from cellman and was just getting geared up to order the lipos as well... until I saw this thread! Just so happens I have about ten laptops at work which are getting thrown out with battery packs- I will have to rescue them. More will be coming through as well which is good!

Just a couple of quick questions- what chargers are being used to charge the packs and in what configuration? I'd be putting together a 48V 20/30ah pack if there are enough good cells. Is a bms a necessity for these packs?