How to Make a 12v Battery for Free


Introduction: How to Make a 12v Battery for Free

This is how i made a 12v li-ion battery for free without having to buy any cells or batteries from the internet what so ever. i use these in all of my projects on instructabals that need a battery of some sort, it is cheaper and can usually store more.

Step 1: Source Your Batteries

One of the best places to get batteries that are no longer used but have large capacity and large power output is laptop batteries, these batteries are usually li-ion as they are the lightest per power output and are good in general. if you have any old laptops that are not used anymore then use them, if you have a laptop with a battery that says not charging, what is the point in keeping it, re-use it. phone batteries are good as well but usually don't have good capacity as they are designed for phones and although have the best power to weight ratio they don't output much power as it is small, these batteries are good for smaller projects.

Step 2: Take the Batterys Apart

This only applies of your batteries are in a case.

I strongly recommend not to take phone batteries apart as under the metal is the cells itself with harmful acids inside.

So first, you take all of the stickers off (make sure to enjoy taking the warranty void sticker off)

After that use a sharp but strong flat head screwdriver to be able to pry away the plastic. i would recommend an old pair of pliers and wire cutters that you don't mind messing up slightly

Pry at the plastic until something breaks, this is one of the hardest parts. If you ever see sparks remove the tool immediately!

After taking the plastic off there will be a lot of other crap inside the pack, only start removing this until every battery pack has been dissembled.

Step 3: Rewire the Cells

So after you have cells and only just cells (I am using the term cells because a battery is more than one cell) decide what voltage you want your battery pack, this is the list of voltages per amount of cells:

Cell / Volage

1 - 3.7

2 - 7.4

3 - 11.1

4 - 14.8

5 - 18.5


Every cell you add the another 3.7v you add.

Be aware that lithium cells can go up to 4 volts and down to 2.9v and don't ever over-volt or under-volt sensitive electronics with specific voltages. to be able to get stable voltages use a voltage regulator like this one:

Now if you want more "power" in your battery pack but don't need volts and you have the same amount or more spare cells, wire them so they are in parallel, parallel is where the two or more cells are in + to + and - to -.

Step 4: Protect the Battery

If you have an abundance of electric tape then wrap them up in that, but if you don't have that duct tape will do perfectly fine, you just need to make sure the + and - do not touch as this will short circuit the battery, this could make it explode or catch fire but it usually lowers the capacity of it by quite a bit.

Check that everything is working fine and charge with the batteries rated power E.g. a 12v battery will need a 12v psu (power supply unit, this can be anything from the things that power computers to your phone charger, just remember to check both of the voltages)



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    What you are suggesting has no overcharge protection and thus can be very dangerous resulting in the cells exploding and even killing the people involved. This happens with mobile phone cell packs and this one above is a lot more powerful.

    Why don't my solders stick? Do I have to file it down or use paste?

    1 reply

    It should work if you tin both of the surfaces then add more solder as necessary. A perfect guide is here:

    thank you

    i will send an update

    correct me if i wrong.

    if i need a 12v battery i can take out the cells from my old laptop battery and use them as is and when i need o charge them i can just connect them + to + and - to -to my laptop charger?

    2 replies

    well not necessarily, if you are wanting 12v then the MAXIMUM voltage should be 12.6v as if overcharged lithium ion battery's are not very forgiving, furthermore you will need holders or solder wires to it and also a charging port but theoretically attaching wires works too but is not very user friendly at all. if you could tell me what it is you were wanting the battery for then i may be able to help a bit better.

    i wont connect the charger's wires directly to the battery. i will solder connector to the battery and connect the charger to the battery through the connector.

    i will use the battery to power up an amplifier for a portable speaker.

    you never ever charge li-ion batterys with out a proper charger a 12 volt unit like pc power supply are wall socket adapter is very very dangerous play it safe get a imax b6 balance charger they are made for charging li-ion packs

    1 reply

    When I said I used a pc power supply I used a PCs AIO power suppply which was 12v 5ah and worked in exactly the same way as a li-ion charger, but just to trickle charge them at the end I used a wall charger which was 12v 500mah and this had an overcharge protection circit. If any of the batteries die they would have been throwen out anyway, just making the most out of them.

    just as a heads up: the linked kit is the kit only without (!!) the regulator itself.
    you need to buy an LM317 in a TO220 casing to make it work.

    also, such a linear regulator will discharge way below 2v per cell if you let it.
    search for 18650 protection online and add one such protector-pcb to each cell if you value your build.