Why does laptop battery show < 100% charge

[Prasan]

> This may be down to the bios software. I run my laptop (a Dell Inspiron
> 1525) off AC power in both linux (F11 and rawhide) and windows vista and the
> battery charge gradually declines over the months, but the battery doesn't
> charge unless I unplug the AC briefly while the computer in on, which
> prompts the machine to charge the battery fully.

I have exactly same functions in my Dell Inspiron 1545 Both in Fedora
11 and Vista Battery gradually decrease % of charge when continuously
even when plugged to AC. When powered off when I plug the AC adapter
battery does not get charge if the battery level is above 95%.