DVDdoug:
Most chargers don't have a programmable microcontroller or software... But yes, it's feasible.
No... The Arduino has a 10 bit ADC (analog-to-digital converter). That gives you 1024 "steps" for 5mV resolution on the 5V range or 1mV resolution on the optional 1.1V reference (too low for your battery).If you are charging in series you'll need a voltage divider, or multiple voltage dividers, to keep the voltage below the 5V maximum and your resolution will be reduced proportionally.
well, that is rather depressing...
Hobby chargers have programmable microcontrollers in them though. its how they have so many features, settings and other things and can often be hacked with custom software (like cheali software)
Wawa:
Is this for lab testing cell capacity (I assume for a 4.2volt cell).
Can't see any other reason why you want this precision.
Leo..
for hobby use. I build drones and my charger balances down to within 0.004 ish volts but that difference can shorten the lifespan of the cells if it ends up being higher than 4.200v, it will increase internal resistance over time and... generally bad stuff. its a very good charger too, but not as good as a 600 dollar charger (which has the accuracy I want) which is so far out of my budget I might as well call myself the president if I could get it. I do enjoy building things and I can balance cells down to 0.0001v with my multimeter but that is tedious and I dont have time for it so I would like a way to just build one myself.