Why not load up a revolver, place it in my nightstand and feel comfortable that in 40 years it will still fire every round.
I say this because in the mid 70s I found a revolver (S&W M1917) in my grandmother's nightstand. She said she put it there when my grandfather went to fight WWII in 1943 and never moved it since then. I took the revolver out to the range, shot the bullets that were in it, fired about 30 more rounds, cleaned it, lubricated it, refilled it with modern hollow points bullets, and put it back in her night stand. In the mid 90s, my grandmother died. I took the pistol home with me and repeated what I did in the mid 70s. It sleeps in my nightstand now. I have another S&W 1917 for target practice, so there is no need to wake my grandmother's pistol up.
the original question was why shoule I place my life on a battery....I merely suggested that you could get a brand new battery every month, obviously that would only apply to someone paranoid about the dependence of batteries.
as far as grandma's trusty fireare...great, I have several myself but you set up a scenario, so I will too.
Your family lives in a middleclass neighborhood in a large city. You leave for work every morning and your wife and young children are at home. Your wife feels secure knowing that she has a handgun and knows how to use it. She knows where it is, very handy to where she is, but in many cases the kids know where it is too. Wouldn't you feel more secure knowing that ONLY she could fire that gun? The kids can't, their friends can't, and in the unlikely event that an intruder got it away from her, ....he can't either.