I connected three Nokia BL-5C 3.7v 800mAh Li-Ion batteries in series for a robot project resulting in 11.1v @ 800mAh capacity. How do i charge the pack? Should i get a 12v 5A adapter and limit the current or get a dedicated Li-Ion battery charger and just connect the leads? If i want to make my own, how to do it?

  • \$\begingroup\$ I would recommend you use an IC built to charge LiIon cells. They are cheap enough and safe. Designing the circuit yourself is not worth the time if you have to ask how to do it. \$\endgroup\$
    – 0x6d64
    Commented Aug 22, 2017 at 10:32

1 Answer 1


You cant simply use your cells when they are in series across the terminals of the outer cells. If one of your cells has(and they are all different) a significantly lower capacity it's voltage could drop below 2,5V and damage the cell before the voltage overall gets too low to shut down. You'll have to use a Lithium Balancer for this to work. It tries to keep the cells at the same voltage while protecting them.


simulate this circuit – Schematic created using CircuitLab

This will evenly charge your cells. I also recommend a protection against over-discharge, overcurrent and backfeed. The Balancer/Charger and Protection can also be combined as one unit.

A board like this has several protections build in: 4A 3S Lithium Battery Protection Chip Board

  • \$\begingroup\$ So ok. Say i bought the 3S Li-Ion battery protection. I would simply connect the adapter leads to the Balancer and the the balancer connect to the batteries as the schematic indicates? The batteries themselves have protection don't they? They were for mobile... What am i missing? \$\endgroup\$ Commented Aug 22, 2017 at 10:43
  • \$\begingroup\$ i1098.photobucket.com/albums/g378/lilianleung/… P+/P- is where you charge it, the cells go between B+&B1-, B1-&B2-, B2-&B-, the positive of the cell always on the first mentioned. Then you can grab the power from the cells between P+&P- when not charging. As stated in the listing: Parameters: Maximum protection voltage ( for every single cell ): 4.255V Minimum protection voltage ( for every single cell ): 2.35V Maximum operating current: 4A Protections: Short circuit protection Overcharge protection Over-discharge protection Over current protection \$\endgroup\$ Commented Aug 22, 2017 at 10:54
  • \$\begingroup\$ I don't know if your cells are already protected, but either way this would be an all in one solution for battery charging and discharging without risks. You might want to find a circuit board that has a lowes maximum current as I'm not sure if your cells can provide that much power. \$\endgroup\$ Commented Aug 22, 2017 at 10:57
  • \$\begingroup\$ Batteries connected in series have the same current. \$\endgroup\$
    – Jason Han
    Commented Aug 22, 2017 at 11:03
  • \$\begingroup\$ True, I corrected the issue, sorry for getting something wrong. \$\endgroup\$ Commented Aug 22, 2017 at 11:06

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