Anything connected to an aircraft hot battery bus does not require the battery switch to be ON to get power. "Hot" indicates that the bus is always powered. The chronometers, amongst other things, run off the hot battery... although this might be a bad example.... The clocks' internal time circuits usually run off the Hot Battery Bus, but the clocks' digital displays may run off other busses... so that the battery is not drained too quickly when the aircraft's generators are not running.
Rgds.
Q