# Big Lithium Ion Battery Pack Made From Used Laptop Batteries (190+ Watt Hours)

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## Introduction: Big Lithium Ion Battery Pack Made From Used Laptop Batteries (190+ Watt Hours)

I was able to get 10 large used laptop batteries for only \$8. I was able to build a 190 watt hour battery pack very easily.

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## Step 1: Removing the Cells and Charging

First pop open the batteries and take out the cells. You can open the plastic cases using a flat head screwdriver. Sawing the corner a little bit helps get the screwdriver in. Keep the parallel groups of cells together.

Measure the voltages and write them on the packs. Arrange the cells by voltage, less than .5, .5 to 3 and over 3.

I charge with cheap transformers I can find. This is very dangerous as you can over charge the cells. Never charge the cells past 4.2V.

If the cell is less than 3 volts you need to charge the cells at low current, less than 50mA. I use walkie talkies that usually charge 3 AAA batteries each. Charge until 3 volt and then switch to high current. After 3 volts you can charge up to 1A per cell. I use a 12 volt 4 amp charger and charge 3 cells on series.

Cell under .5 often have problems.

## Step 2: Connecting the Cells

Lithium cells are great But you have to keep them between about 3 volts and 4 volts.

When you build a pack arrange the cells in parallel and series groups to get the amps and volts you need. Most laptop cells are 2200mAH and can be discharged safely up to 1C (2.2A for one hour).

For my pack I have 3 sets of 8 parallel cells in series. So my voltage is 12 to 9 and my max current is 17.6Amps. This works well for powering cheap car 12V motors. If you want more power you can add another series set and get 16 to 12 volts.

It is important that each series set has the same amount of parallel cells.

First tape your cells together in the parallel sets. Then tape the sets together alternating positive up positive down and tape it all together. I used small nails to connect the packs. Cut off the nail head, sand it and the top of the cells and solder the nail to the packs. I kept the 4 cells together from the packs. When soldering on the positive side it is super important not to get solder on the sides of the battery top. The outside of the battery is negative so the cell will short out.

I also soldered 2 14 gauge wires to the positive and negative sides of the battery. I taped the wires down so they couldn't be pulled of the battery.

## Step 3: Battery Box and Padding

I glued some fibre board pieces together to make a box. I folded some padded fabric and laid it in the bottom of the box.

I rapped the battery in fabric and placed it in the box. I stuffed more fabric in the corners so the battery was secure.

The fabric helped with reducing shock and vibration but the battery can get too hot because its insulated.

## Step 4: Measuring Cell Voltage

I wanted to be able to measure each parallel set of batteries without taking the battery out of the box. The first set can be measured using the negative wire and the top of the battery. The last set can be measured using the positive wire and making a small hole in the batteries plastic. You can stick a prob in this hole to measure the negative. If you measure the total voltage and subtract the two cells you will get the middle voltage.

## Step 5: Testing in the Prop Bike

I installed the battery in my prop bike and it works great.

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## 13 Discussions

So is there a link or something you could give to show us where to get dead laptop batteries for cheap? I was hoping to build my own bank, but all I see is the ones on eBay and they are \$50-100

Were you able to find used cells by any other means? I am currently in the same situation and seek to avoid eBay if possible.

How did you get the cells? I'm having trouble obtaining the used laptop batteries

i want to make a 2S battery pack by connecting two laptop lipo batteries in parallel and connencting those in series with another two lipo laptop batteries connected in parallel, what i am confused about is where to connect my balancing wires in case i wanted to charge them through a balancing charger, could anyone help me with that ? taking into consideration i know how to charge lipo batteries connected in series through a balancing charger

I did the same thing to power my homemade boombox (please check it out, i did an instructable on it) i used 48 cells to power the speaker

Folks: Don't charge in series without balancing. Instead consider charging them all in parallel. That way, the problem of mixed cells with different age and condition is not a risk like it is with series charging.

Lame, I know, but you only need one cell to go bad to put 6V across the other two which would be... sub-optimal.

I'd track down the spec sheet on the cells, just as a double check. My middle name isn't danger. :)
Just wondering, how many of the cells from all those battery packs were bad?

Ya I am too cheap to buy a real charger. I charge with a 4A max 12.3V (open circuit) transformer. The current per cell is less than .5A (.25C). Also the amps drop as the pack gets close to 12V. I couldn't over charge the batteries if I left them charging for days. I also check the voltage of each parallel set to
Make sure they are balanced.

I like doing things cheap and dangerously ;)

Good! Danger is my middle name too :)

But FYI, you can get Li charger modules on ebay for about \$1-5.

This is a very good use of old laptop cells. I've found that often the laptop battery controller is set to simply shut off after some number of charging cycles regardless of the state of the battery (at which point your laptop thinks it has no battery!). One word of caution: you should have some monitoring of your batteries, esp. when charging. With so many so close together you can have a nasty explosion if you overcharge or overheat those beasts!