ibook G4 Trouble!!!

Hi guys,
I got an ibook g4 one of those late 2004 models last year and have never looked at another laptop. it was a hand-me down, but one of the best things i have ever owned i love it with all my heart but i am facing a battery problem, it says 0%, icon says charged and the charger is green... the day before it charged up to 5% the icon was showing red (kinda like running on reserve) but i used it for 3 hours before it died on me... but the situation has deteriorated to 0%????
Plus i have a space issue, i always get one of those 'your start up disk is almost messages' especially when i use photoshop... i wanted to verify the disk but turns out it cant be done in panther???
HELP!!!!!!
P.s; i am from a small country where going to a mac store which i only one, would demand my liver... i need to assess the situation before i can sell my liver... a mac is worth it!!!

I thought about getting tiger, but i figured leopard is better, but its really expensive and with the trouble my ibook is causing me, i want to make sure its still good before i invest this money.
Could be old age??
How do i know if its crashing??
How do i verify my disk, that option is kind of invalid in disk utility???