My SG550 is 6yrs old and still runs like a champ as long as you feed it good batteries.

To check voltage you need a meter.
I have a digital that cost about $75 but you can get a cheaper model at like radio shack or even Lowes. Digital is more precise in telling you exactly how many volts the AA is showing.
They should be more than 1.5 new. Engergizer Lthiums are almost 1.7v when new.
Once a battery gets to around 1.2v the cam will start to act weird until they all are that low and then probably not power on.