I have a project in mind based around a Raspberry Pi Zero. The case I am using has slots for two AA batteries so I thought I would use some of the AA sized Li-ion batteries.
The batteries I want to use are 3.7V 2300mAh.
The charge circuit I found is: http://www.banggood.com/37V-Liion-Battery-Mini-USB-To-USB-A-Power-Apply-Module-p-928948.html
Ideally I would like to have two batteries in parallel so I could get 4600mAh, but I know there can be issues charging and discharging in parallel, plus I have no idea if that charge controller will do that.
My next option is to just use a single battery with that charge controller, that seems the easiest. Although I cant actually find any reliable info saying this circuit can charge Li-ions, Can I use anything advertised as charging Li-po on Li-ion?
One other option would be to put the two batteries in series and an LM7805 to bring the voltage down to 5V, would this be suitable? I would use an external charger that way.
Sorry for the broad question, if I use google all I get are things for Li-po batteries, and if I look for Li-ion charge modules all I get are the external type.
I am pretty good with amateur electronics, but I've never worked with these before and I don't want to get it wrong.
Best Answer
You are asking about the different ways to charge a 2S1P (two batteries are connected in series) and a 2S2P (two batteries are connected in parallel) battery pack. Use these terms when researching this subject.
The better battery chargers will balance the charge over all the cells in a pack. And will tend to charge the batteries faster near their charge rate limit. They should also stop charging when the batteries are full. Detecting the end of charge depends upon the battery chemistry and manufacture's recommendations.
The cheaper battery chargers will not bother with balance and will (should) charge batteries at a fraction of the charge rate limit. If they charge the batteries slow enough they may not bother with checking for end of charge.
You should avoid using linear power regulators when using batteries. Linear power regulators regulate by appearing as a resistance between the load the battery. It is clear, using this paradigm, that such a regulator will convert power into wasted heat. Instead consider a switching power supply.