In article ,
Charlie Self wrote:
One less excuse. I just now checked the price of the battery powered emergency
lights: around $30 to $40 each. The more costly ones are halogen, last for
about 90 minutes.

Time to install a couple.

And yes, they do need an electrical circuit to operate, both for charging and
for sensing power failure, AFAICT.

Absolutely correct on the need for mains power. The batteries 'float' on
the charger, so they're always fully charged. And the unit has to 'see'
the power line, to detect when the power 'goes away'.

They do draw a few watts when the power is on; it's a small draw when the
batteries are fully charged.