Actually the CPU doesn't tick at all if there are no timers about to expire.

When the time to the next timer firing gets large enough, the CPU clocks and voltage are switched off, completely halting the CPU and dropping power consumption of CPU to near-zero. The RAM is kept alive, and the CPU eventually gets woken up by an external timer or external IRQ, to process whatever app requested to be woken up..

So yes, if you have a timer that fires every 100ms, there will be a significant impact on standby battery life. XChat used to have a periodical 1-second timer (IIRC), and when the maintainer managed to get rid of it, battery life improved significantly for me :-)