I'm currently designing a small application with a bipolar power supply. As the circuit needs to be portable, I've included two Li-ion batteries in series with the midpoint grounded to generate the positive and negative supplies.
I need the batteries to be able to be recharged without removing them from the circuit, but I'm having trouble designing the circuit to charge them. Initially, I thought about adding a DC input followed by an OPAMP-based virtual ground driver to split the DC voltage into a positive and negative rail, and use each rail to charge each battery using some IC like the MAX1555, but this would only work for the positive battery.
Is this the best approach, or is there some other better way to accomplish this?
Edit: A 12V wall adapter will be used for the DC input. Also, the device will be connected to an Arduino board using a different power supply. The device will not draw the same current from both batteries.