Please help about battery

[mypocketpc]

My hx2410 didn't alert when battery was lower 20%. It had been turned off immediately. This was not happened before. :(
Thanks for your help!!
My devices:
hx2410
CF 512MB (3.3V) Kingston
SD 1GB Sandisk Ultra II

[Darius Wey]

It's likely that an application blocked the display of the notification. Were you playing a game at the time, or perhaps something else?

[mypocketpc]

No, I tried to do nothing at that time. In formerly, it’s still alert even playing game and alive until <10%. Maybe I must substitute a new battery. :( :?