You do not necessarily need electricity to fire a flash bulb.

All need some explosive to start the combustion of the metal filling. This explosive is typically ignited by an electrically heated wire.
But there was one type, designed during the type 126 phase with the explosive being ignited by mechanical impact by releasing a spring.
One saved partly the space for the obsolete igniting electrics, but moreover one got independant of an aging battery.

However succeeding flash bulbs were electrically ignited again.