Battery Level on PX-11

[knife31]

Purchased a PX-11 about 5 months ago and really haven't used it that much and my battery died. I didn't check the level when I received it, and it could have been low at the time. Does anyone know what the expected life should or would be. It's my carry around calculator for simple stuff grocery stores etc... I didn't get any batt low indication, however as I said I didn't use it that much so it could have yelled loudly, and I wouldn't have known.
Randy

So, I just looked at the manual and it says a couple of months. But I think I have a total of an hour of use, so don't know if that's normal or not.