Is there someone her more knowledgeable who might be able to answer this question:
Is it usually the case that there is just one type of battery fitted across a particular type of airliner? Would this differ by version (i.e. also say a -800 vs. a -900) and by customer spec?
What I am driving at is that it would be very shortsighted of the manufacturer to build a charger compatible with only one specific battery type - be it chemistry or capacity. So perhaps retrofitting a different type of battery as an interim measure with weight penalty is a straightforward option?
I presume what Boeing is struggling to do at the moment is work out what actually did go wrong as the issue might not be in the battery itself.