Replacing battery cells in power tool battery packs

Discussion in 'General Electronics Chat' started by Gdrumm, Oct 9, 2014.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    A friend is planning to purchase some cells to replace the dead ones in his power tool battery pack.

    I tried this once, with minimal success, and the new cells didn't last but about one year.

    Two questions:
    1. Are there cells available that have a good / best life expectancy?
    2. Are there any tricks to soldering the leads positive to negative, etc.?

  2. Lestraveled

    Well-Known Member

    May 19, 2014
    - Yes, they are out there. Ebay or a battery rebuild shop.
    - Get the batteries with the solder tabs. Make sure you don't heat the battery up too much.

    Here is a company I have used before. Very fast delivery and good batteries. They also have a phone number that works.
    BR-549 likes this.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Tabs must be spot-welded to the batteries; they cannot be soldered without screwing up the cells.
  4. MrAl

    AAC Fanatic!

    Jun 17, 2014

    I have to agree fully with the other replies. The batteries to buy are the batteries with "tabs" welded to the ends of the cells. Some battery outlets let you order the cells with or without the tabs, and maybe charge a tiny bit more for the tabs. The batteries with the tabs are the only ones that should be soldered because soldering directly to the ends of the battery could mess up the battery inside and degrade the performance right off the bat.

    The "sub C" nicad cells are the typical cell in power tools, but recently they also have lithium ion cells for use in some power tools. For the lithium ion type cell though you really should get the higher end type cells that are made for high (30 amp) discharge, not the run of the mill Li-ion cell.

    If you get quality cells they should last for a while, but it also depends highly on the type of charger being used and how often they are charged. The best bet is to charge only when necessary and definitely not to charge 24 hours a day 7 days a week as that will deteriorate the cells such that they dont work well even after 1 year.

    The power drill i purchased several years ago came with two battery packs. Seemed nice at the time, but within 6 months they were both unable to take much of a charge. I replaced the cells with pretty good cells, and upgraded the charger to charge once per day with a short charge time (like 15 minutes) to keep the cells charged up (that's the right way to do it). I got 5 years out of the cells that way. But after that 5 years i decided that i did not want to spend another 40 dollars just to get maybe a 2 ampere hour replacement pack (the sub C cells are around 2 ampere hour cells) so i went to Lead Acid.

    I was lucky that i had a drill that could run on a 12v lead acid battery with the addition of a 35 amp series diode to drop the voltage a little.
    So i ripped the cells out of one pack and replaced them with a high current diode, and connected a long cord to the pack with connectors on the other end that would plug right onto a regular lead acid battery ("Faston" terminals). Now i have a 8 ampere hour battery rather than a 2 ampere hour battery pack to run the drill, and i can switch to a second 8 ampere hour battery by just unplugging and plugging into the second battery.
    It's never worked better and the price was about the same for the one battery.
  5. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
    Thanks for the good information.
    I forwarded the link to my friend, along with the safety instructions you've provided.