DIY Charging a Craftsman C3 Lithium Ion battery pack

C3 Battery
To charge DieHard / Craftsman C3 lithium-ion battery packs apply 21V across the + and – terminals. (rounded end = +, opposite = -)

C3 Connector C3 batteries come in several variations and each one has different requirements to allow charging.   Most variants will need a 22K resistor between the left terminal (when looking with the curve away from you) and the + terminal.

Be sure to use a current limited supply to avoid the possibility of damaging your pack or starting a fire should the internal protection circuit fail.

My model was a 315.PP2025 (130211023) rated 19.2V, 48watt hours purchased in mid 2016 and required the 22K resistor between the left terminal and the + terminal to charge without cutting off after 30 seconds.

22K is red red black black brown for 1% 5 band resistors, and red red orange gold for 5% 4 band resistors.

C3 Circuit For charging in the house, I’ve got a 24V 0.5A wall wart (more of a brick) power supply and an LM317 regulator in a TO220 package.  I used three 10 ohm resistors in parallel to spread the heat out so that I could use 1/4 watt resistors without getting them too hot.  (The LM317 will get too hot to touch, be careful.)  The circuit is to the left and limits current to 375mA which, for my 48W pack, is a nice gentle 6 hours charge from empty and generates no heat in the pack that my IR thermometer can detect.  The LM317 will go up to 1.5A with a big heat sink and seven 5.6 ohm 1/4 watt resistors in parallel, but be careful to not charge packs that are below 5V at this high rate.  The 1.5A charger will fill the big 48W pack in 1 hour 40 minutes.

The 375mA charge rate is safe for even deeply discharged batteries that won’t charge in the Craftsman charger.

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2 thoughts on “DIY Charging a Craftsman C3 Lithium Ion battery pack

  1. Tony Snow

    Thank you for the detailed information on charging a 19.2v Craftsman battery. I also purchased my batteries mid-2016 and am having problems with the charger. I will use a DC power supply to charge them from now on. I have a question for you if you do not mind answering it. Using the diagram you have that is red, my battery is identical in appearance but I am getting mixed results on output. If I connect a multi-meter from the 21v terminal(+) to the ground(-) I get 4.29 volts in the batteries current state. If I connect the 21v(+) to the terminal deemed (no connection) I get 16.65 volts. I just used the battery yesterday until quit operating the tool being used. My question is: do I use the stated 21v positive to the ground to charge or is my battery slightly different and will I use the 21v positive to the “no connection” terminal? Any help will be greatly appreciated.

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    1. chisight Post author

      Tony Snow, if you have voltage on your “No Connection” pin relative to any other pin, then you have a different pack with a different internal controller board than I do. It would purely be a guess that using the +, -, and 22K terminals could charge your battery and that the 4th terminal is not used. The internal controller board in yours might be close enough to mine to protect your battery or it might not. Be careful and watch out for the magic blue smoke.

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