If you don't mind me asking, why in the world do you own three cameras of the same model?
When I bought my A540, my wife and daughter immediately liked its large LCD screen and quick focus and wanted ones of their own. Several years ago I got tired of being told what to take pictures of, so I make sure they have their own cameras. Our previous cameras were an A40, S200 Elph and A60. Only the A60 was a battery hog, but not as bad as the A540.
I sure hope others take the time to tell of their battery life. I have a support case open with Canon asking if they could do a firmware upgrade to lower the low battery shutoff voltage point. It is a longshot that they will even consider it, but if I can point to user comments, it will help.