I have JS5IN1 (jump starter) which hasn't seen the light of day for some
time. The battery is flat, the worklight come son quite brightly but
otherwise nothing. I have attempted to charge it using it's own charger
plug with little result, the compressor will run for a short time but
that's it.

I have a "smart" battery charger the instructions of which suggest it
might be able to revitalise a flat battery. Can I connect this directly
to the JS5IN1 across it's jump cables without doing any damage? Taking
the battery out to charge it would probably be a better option but none
of my screwdrivers will fit the screws I assume hold the case together.

There is a lot of varied expertise in this group so any thoughts?

Thanks.