Perhaps it's a wiring issue causing the battery to dump and by virtue overheat/burn the battery. A plane that's more 'electric' than any others before it may be subject to wiring snafus. So the "same" battery that works in the conventional plane is put under a faulty load causing it to overheat. Tracking down a wiring snafu in 100 miles of wiring snaked through the fuselage of a finished plane might not be the easiest or quickest task. Bottom line is the argument with BA will be whether this becomes a quick/simple fix or whether the burning battery is the symptom of a bigger issue yet unknown.