Battery Charging Problem? Options

[ptoki]

I had netwalker unused for a while. After plugging it to charger and booting it started to behave oddly.

Netwalker works fine but charging led (the one on netwalker) blinks and unit will not charge more than 70%.

When booted from halt witch charger unplugged it shows 10-12%. After just plugging charger and unplugging charge jumps to 70%.

I had left it charging (with blinking) for over 24h but it behaves the same.

Can any one suggest what happened?

I wanted to use it as small home media center for music and internet radio and for email but now I dont know how it will behave.

[ptoki]

Deluxe, thanks for suggestion but i think that cells are fine.
Netwalker was running long on batteries till some time ago.
Then was unused and then it started behave oddly.
So I think that cells are fine. But thats just my unprofessional opinion.

The way I thinked out is that I will buy external battery for 12V with charger.
I will plug it other way around so netwalker will be without battery and this new battery will be plugged as main power.
I think thats most safe and unproblematical way.

But first I will try to ask for advice guy which pointed by ArchiMark.
Just to ensure what might failed and how much would it cost to repair it.

Thank You both for constructive suggestions.