How to connect two batteries in parallel and in series?

Question

Electronics

There are two batteries, 3.7v 200mAh each. You need to connect them in a combined way so that you can charge them through the charge module. I can't figure out the diagram

Answer 1

I can't figure out the diagram

Well, here's your diagram.

Take a toggle switch for two positions and two directions, and connect as shown here. In one position of the toggle switch, the elements will be parallel (this is for charging), in the other they will be in series (this is for powering the load).
But in fact, there is a much more convenient way in which you can charge both elements from a regular smartphone charger without switching them. You buy on Aliexpress just such a battery Krona :
Inside it are two lithium cells and a scarf with a balancer and a step-up voltage converter. You delete the standard elements and connect your own instead of them (the connection will be sequential). Then, plug the cord from any mobile charger into the microUSB plug on this scarf. Next, watch the color of the glowing LED. Red - charging in progress, green - charging completed, the charger can be turned off.
By the way, Ali offers a lot of lithium Crowns, according to my link, this is not the only one.

Answer 2

In parallel - just connect together and charge as one 400 battery. In
series - you need charging with balancing, connect +/- and a balancer in the middle.

Answer 3

Perhaps you want to charge with a charger for 3.7V and after charging use a voltage of 7.4V?
In this case, use special chargers. If they are not, then you can come up with on the basis of those that are, i.e. take a charger for two batteries and charge them separately. When charged, connect both batteries in series with a transistor. But at the same time, it is desirable to put a diode on each power channel so that the current does not run back. The signal to pull the transistor can be taken from the battery charge indication.