On February 25, 2018 at 10:51, DIYJeff said...
Is there something about some "compatible" batteries that can cause problems?
The NiCd batteries used in Pronto are fairly forgiving with respect to charging details, Lithium batteries are very fussy. Mismatched charging on NiCd might reduce battery life, mismatched charging on Lithium batteries can cause fires. This is why one should be careful when replacing Lithium batteries with a 3rd party "equivalent".
Aging batteries cannot deliver full peak power. It is possible that the battery in the problem Pronto has reached this point.