Charging 2 LiPos in serial used as split rail
Since lipos can be very dangerous, and 'assuming that I disconnect the batteries from the rest of the circuit first' doesn't lend much confidence, I advise you make it as fool-proof as possible.

Adafruit has a decent article on multi-cell charging, of which I'll reproduce here.  Basically, you'll want a 3PDT switch (not abundant, but available) to switch between connecting the batteries to the load and to the chargers.



Otherwise, you could just remove the batteries from the circuit and charge them.  Whichever method you choose, again, I advise not to assume that the operator (you or another user) remembers to hit a switch in order to avoid a potentially unsafe state of the batteries.