I want to make a custom lithium-ion 18650 standard cell charger as I will be charging 100s of them (recycling old laptop batteries). Base on my research, lithium-ion cells use constant-current, constant-voltage charging. I'm thinking of using 5v and PWM using an Audrino with a feed back loop to maintain the constant current and voltage. Will the PWM ripple cause any damage to the Lithium ion cells? Is there any major short coming to my thinking?
The cheapest way it to get a CC/CV Power Module from ebay.
If I needed to charge many cells I'd get 10-20 of the cheaper modules and create a rig with those. They have decent LED indicators for how charge is going.