MarkT:
Perhaps you should be more clear about what actual hardware you have and what you are trying to do,
+1
I don't see why you need a negative supply to generate a voltage down to 0.0volt.
And why you need zero volt to charge batteries.
Opamp outputs can't go down to 0.0volt, but they can drive a power transistor that can do that.
And there are opamps that can measure to (and below) zero volt on a single rail supply.
Post the diagram of your "charger".
Leo..