In article , lid,
vaughn says...

I've been renting Cessnas for ages but always avoided using the "cigarette
lighter" power outlets, especially on planes with 24-volt electrical systems.
This is getting to be a bigger and bigger problem as I accumulate more toys, so
my specific question.. (Sorry if it seems hopelessly naive)

Is it safe to charge my IPad in a 24-volt 172?

I believe you are talking a USB charger? (is a cig lighter male on one
end, and USB on the other). NO! it won't work.

Either... get a third party cig lighter/USB adapter designed for 24v, or
perhaps you might have to get a 24v=12v 'car' voltage adapter, and rig
it up in it's own wee box (to make it tidy), with a cig plug (male) on
one end for the plane, and a female cig plug on the output side, and
plug your Apple USB adapter into that. (You should also check the
polarity is OK on the plane too!

--
Duncan.