...It tends to happen when the batteries are old and failing, so it may be something to do with damage trying to charge dead batteries. I always advise removing failing batteries ASAP.
I was planning on buying a replacement battery but now... I should buyi another Powerbook.
PowerBook 5.2 MorphOS 3.11
PowerBook 5.8 MorphOS 3.11
Amiga 1200 BPPC/BVision AOS4.1 FE