Depending on how often you use it,4 months at a time maybe?The last time I changed mine was in April and it's still running.I think Energizer batteries last the longest,never buy Sunbeam batteries,they don't last long.
Depends on how much you IR connect with another tama or send stuff to it usin the IR... I've seen some people say month and a half sending like crazy to... probably about that 4 months... maybe more if you completely ignore it...(Batteries in, no play at all)