The discharge and charge profiles of the new combined battery have to be created from scratch, as we can't just use the single battery profile as it's no longer valid. This means your super-accurate profiled time-to-discharge reading gets reset to the default 2 hours until enough discharge and charge data has been automatically collected.
So, what about the following warning dialog? Flames / suggestions as comments please.
p.s. I still can't test the multi-battery code, I'm still looking for donors.