Saturday, August 6, 2011

Soldering mobile phone batteries

There are lots of warnings online about doing this - 99 percent of which come from other warnings about doing this. Viral behaviour.

But they aren't without caution - lithium fires happen.

I had a lot of old mobile phone batteries to waste, a 25 watt soldering iron was perfect for joining them up in parallel. I'm hoping they will make a nice range extender battery for my bike if not discharged too fast....

Keep a big bucket of sand handy - if you do try this  - at your own peril.  No liability accepted.

30 volts, ten ampere hours in theory.


  1. Awesome! How do you charge this battery pack when all the batteries are soldered together? Would connecting a simple 3.7V battery charger work? Or possibly wiring up an old cellphone in order to charge it.

  2. Hey, thanks for the comment.

    You should never connect 3.7v from a power source directly to a LiPo cell to charge them. You'll need a dedicated charger that charges each cell up slowly to 4.2 volts each, then when it reaches that voltage it drops the current as the cell's resistance rises. Dedicated chargers arent very expensive any more.

    The reason mobile phones have simple wall chargers is that the charging logic is built into the phone. Important.

    You should never discharge a cell below 3.7 volts each or damage will result to the cell and it's life will shorten.

    Incidentally there are 8 cell packs in the photos above. So it would be called an "8s pack". Eight in series. Each one having ten batteries. So ten ampere hours total because it's one ampere hour per battery.

    So when fully charged it would be 8 times 4.2V equals 33.6 volts.
    it would be considered empty at 8 times 3.7V equals 29.6 volts. You could use more but shorten the life considerably.

    Some good info here under the 'charging' section:

    And some great info on LiPo chargers in the hobby world:

    Hope that helps.