I have a couple of dashcams, both of which have internal batteries. Both
have worked well and neither has, as predicted online, exploded in the
sun.

Both vehicles have permanently on cigar lighter sockets, and I used to
leave the cams to fall into parking mode - 1 frame per second.

This year both internal batteries have failed, and I'm now feeding each
via usb adapters that measure the current taken, voltages etc. This has
slightly alarmed me with the ddPai cam, which is taking 0.6A at 5 volts
in either mode in a car that I'm using less, and is pulling the main
battery voltage down to about 11.5 volts or less at the end of a few
days of little use. The cheaper cam takes 0.2A.

The question isn't that, though. As summer may be coming, I'm thinking
again about the dangers of leaving these things powered up in hot sun.

Is the thermal runaway that causes these lithium batteries to swell and
burn not likely to occur in an electrically dead battery or is it a
chemical effect that occurs with or without volts present?


--
Bill