Sudden, sporadic car battery problems?

I drive a 2005 Honda Civic Hybrid and for the last several months on rare occasions(maybe once every couple of months) when I go to start my car it hesitates to start and the red battery light on the dash comes on once it does. The battery light will go on and off as I drive, usually on when moving under 10mph(including every time I stop) or in the 40-55mph and off when accelerating at speeds out of those ranges. When driving it with the battery light on it seems to drive a little 'weird' but it's hard to describe that any further. If it starts up with the battery light on, if I turn it off and leave it off for several hours before starting it again it will start up as normal, the battery light does not come on and all seems normal until the next time.

I went to autozone and had the 12v battery checked a while ago when the battery light was NOT coming on and car was normal and nothing appeared to be wrong with the battery. However, today when I started my car to leave work the red battery light came on and car was being a little funny so went to autozone and again had the battery checked and for a second the reading seemed normal before it came up saying "Bad Battery" and "Replace Now".

I honestly have no idea when the battery was last replaced and did go ahead and buy a new battery, but as I know very little about cars I just wanted to ask if this sounds about right for a 12v battery failure? Could there be other underlying problems or is it most likely just an issue with the old battery that the new one will resolve?

It is a hybrid car, so it also has an IMA Battery, but that appears to be functioning normally and I believe it has it's own distinct separate warning lights on the dash for when it has issues.