Dell Latitude D600 battery Won't Charge - Motherboard or Battery?

Just trying to see if any of the good fellows in here could help me out at all.

It's a D600 running XP, think about 5 years old.

Recently there was a problem with the DC power connection. Basically it wasn't charging the battery, the light on the charger was going out when I inserted the AC power into the laptop, and eventually it wouldn't turn on at all. I eventually got it fixed, turns out that the DC power connection was bolloxed and had to be replaced.

So now there is a new problem. The battery won't charge at all. The laptop runs fine on AC power though. When I go into the Bios it says that the battery's status is "charging". When I check in power management it says that the battery is charging but is at critical level, ie. under 3% (actually 0%!!) I take the battery out, leave it for a while, then reseat it and the charging light comes on on the laptop, at least for a while, then goes out. The battery light is constantly flashing/flickering too, making it look like it's power is being accessed, but of course it isn't.

Sooo. It looks like it could be one of two things:

1) It's the motherboard circuit that routes power from the AC connection to the battery, thus charging it, that is broken, or

2) It's the battery that is dead.

What do you reckon? Bearing in mind I don't have a second battery or laptop to test it.

Cheers,
Karl.

EDIT: Also, theres no heat coming from the battery at all, nor is there any lights when I press the battery test button.