I've got two LIR2450 rechargeable 3.6v coin cells. These need to be connected in series to form a 7.2 volts which is being regulated down to 5v to power an ATMEGA328P. I need to charge the two batteries using a USB power supply. As USB can only supply 5v, I can't use this to recharge the two batteries when they are connected in series, as this would require a 7.2v source.
I've found a charging circuit which works well on the LIR2450. If I can have the two batteries connected to this in parallel, it should work, but I can't figure out how to change the connection from series to parallel when the USB is plugged in.
Here's a picture of what I've got so far:
Basically, when the switch is off, and the USB is plugged in, the connection between the batteries needs to become parallel, and remain this way until the USB is unplugged. Any suggestions?