In hard wired models, battery only providing back up in case of AC
power loss.
Alkalines are fine in smoke alarms, and my data shows with good makes
ie Duracell Ultra they'll last nearly 4 years; so well worth cost.

Manufacturers manual will list recommended types; lithium batteries
may also be usable provided their use sanctioned in user guide.

Wouldn't suggest otherwise as these alarms have extra component to
allow for mis fitting of lithium battery ie reversed polarity;
they have potential to explode so why this is so important.

Never use rechargeable loose batteries, as have wrong dischange
characteristics, and would not activate low battery beep as
required [for min 30 days in UK].
Low battery triggered when voltage hits 7.4V.

Difference in Ion & Optical {Photo} been explained by other posters;
Ion now banned most of Europe, except UK & Eire.

Useful info on type selection/location at
www.smoke-alarms.co.uk


"oreo123" wrote in message ...
What is the difference between photoelectric and ionization smoke alarms?

I know that ionization is used within 15 or 20 feet of steamy bathroom or
kitchen cooktop.

TIA.