Li-Ion Battery Pack




Introduction: Li-Ion Battery Pack

Hello everyone

I have been building stuff since i was a kid but surprisingly this is my first instructable. So, I am gonna start with something simple yet amazingly useful and powerful.

Li-ion batteries are used in laptops and cell phones. We can use them in our projects as well. They are so hell powerful :) but again they are so hell expensive :(

The photos show a 11.1V 2200mAh LiPo (similar battery) which costs Rs. 2000 (Indian) and a Li-ion which costs $26.99.

Don't worry ladies and gentlemen, I'll teach u how U could build one of these deadly monsters and show off to your friends. In India, I could build a 11.1V 1020mAh Li-ion pack for a around $3.

Let's get started :)

Step 1: Parts

Let's get the parts ready

  1. Cell phone batteries- 3 pcs
  2. 2 JST connector- 1 pair(1 male and 1 female)
  3. 300 mm JST connector- 1 pc(female)
  4. Electric tape
  5. Soldering Iron- Pointed tip
  6. Soldering wire and flux
  7. Wire stripper
  8. A pair of scissors
  9. Nose pliers

The type of cell phone batteries you choose will determine the performance of your bettery. From a local vendor, I managed to get each 1020mAh cell for Rs. 50 (Indian) which is less than 1 US Dollar.

JST is just a fancy name for a type of connector. The reason we are using them is that most Li-ion or LiPo batteries available for project have those and so do their chargers. They add a bit to the cost.

Also the charger is expensive. If you can manage a cost-effective solution, go for it. I am planning to put another instructable to build a cheap solution for you guys.

The soldering needs to be done carefully as there is high chance of sorting the battery terminals while charging which can damage the cell or even cause burn. If so, put the burnt hand under cool running water for a couple of minutes and ask your girlfriend to call for a doctor.

Step 2: Open Up Your Batteries

This is slightly tricky. If you have damaged batteries, try out on them first.

Use a pair of nose pliers to press and remove the black piece of plastic on the top of each battery. There is a circuit enclosed inside it. For this project it doesn't matter if you happen to break it while removing the plastic. It's easier if you carefully break the plastic by pressing. However, don't let the terminals break. Once the circuit is slightly out, use a soldering iron to remove connection between battery terminals and the circuit. Ensure that you don't short any two metallic parts on the battery with the pliers or soldering iron(by metallic parts, I mean the battery terminals or the body (inside the sticker with company's name).

I broke the circuit while I tried on a damaged battery. Once I got my hands on it, I could carefully get the circuits out as well (I broke the plastic in the process). Who knows when they may come handy.

In the figure, the battery on the left has its plastic broken, circuit yet to be removed. The right one has the circuit removed.

Step 3: Add Tape for Safety

Cut tape in half and take a small strip of it. Put it around one of the terminals. Do the same with the other terminal. This is to avoid contact of terminals with metal body.

Step 4: Connections-circuit Diagram

Most of you will be familiar with circuit diagrams. They show you how the components are connected to complete the circuit.
Here's how you need to connect. All the 3 cells are to be connected in series. For balanced charging (this method ensures that no cell is overcharged), 4 outputs are taken from each node of the battery pack. The charger which I use has this cool feature of balanced charging for battery packs. If you use a normal charger, you could leave out those four wire going out to the 4 pin JST connector. Connecting the wires in the correct manner is very important. In female JST connectors, there are two notches on the plastic head, you can see them facing up in the diagram on previous step. The first is the 2 pin female, the black and brown wires correspond to Black (-OUT) and Red (+OUT) in the diagram. The second is the 4 pin female, they should be connected as: Orange-Red-Brown-Black on the photo to Black-Blue-Green-Red in the diagram. You JST may have different coloured wires, so keep the JST heads with notches upward and match the wires accordingly. Trust me, you won't regret double checking your connection when you see another guy blowing up his stuff for being in hurry.

You should put tape in between two cells to avoid short circuit.

Step 5: Give It a Classy Look

You are almost done now. Just cover it up using electric tape.

Step 6: Test It

Charge it and you are bang on.

The two pin JST connector is where you will get the output (brown +, black - in my case).

The battery provides more than it promises. 3x3.7v should give 11.1v, yipee!!! it shows 12.35v.

It provides good power. You can see sparks coming off when the battery was connected to a big DC motor. I connected the battery to a plastic gear and it spun so fast that i could cut wood with it, and the gear was totally worn off. One of my friends had a tiny spot of burn while using this, don't worry you just needa be careful.

You can also get lesser voltages (3.7 or 7.4, actually around 4.1 and 8.1) by taking the output from two pins of 4 pin JST connector.

I will try to post some cool pics of it blazing off.

Till then, enjoy making :)

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    1 year ago

    The current limitation is important to mention for safety. Don't overload these batteries. In the picture he runs a big motor which surely must have +5A startup current, these batteries were never designed for that type of application. The big difference between the 2200 mAh battery pack in the picture ($13) and this is that battery can output 55 A of current (77 A peak) while this should output around 0.6 A. For low power application this is a great solution but not for larger current applications. The battery may become very hot and pop/burn. Just be careful with Li-ion batteries is all I'm saying.


    1 year ago

    Thanks...Super !!!!


    5 years ago

    Junkskter bhai mere pas batteries to hain buy idk what kind of a charger i must use...the lipo,liion smart chargers are very expensive u know...and can u tell the weight of the 3s battery u made.?


    6 years ago

    Cool :) i want to give a try XD .. but how do i charge it ?


    Reply 6 years ago

    I will try to post a instructable for the charger soon. Currently I use this (but it's expensive):

    One easy way out is to use three general purpose phone battery chargers and connect them individually to each cell in our pack (through 300mm JST connector). You could also charge them one by one with just one such charger.

    That's a bit messy, if u ain't in hurry, i'll be back. Else, there are many people who have uploaded charger circuit diagrams. Good day :)


    6 years ago

    Thanks for sharing this!


    Reply 6 years ago

    Welcome. More things coming, Instructables seems so simple and useful :)