Compaq Presario R3000 power problem

[NanoDuke]

It seems that I was a bit too hasty in buying a cheap laptop off eBay. The description told me that the laptop only had intermittent power through the AC adapter, but it's got a brand new battery.

For the first few days it was working fine, except for the power jack. If I'd move the cable it'd shut off, and take some jiggling to get going again.

I followed some instructions in this thread. And managed to resolder, to the best of my ability, the power jack back onto the board.


Problem now is that the lappy runs 100% fine off the mains supply, but fails to boot from the battery. When the cell is in, it says it's charging, but has stayed at 12% for the last few days.
In the above thread one guy mentioned that the Intel-based model of my laptop (which I have) has a solder joint on the other side of the PCB on the positive terminal. I could only get access to the main joints on the bottom.
My question is, is it possible the the other side of the mobo (that I don't have access to) is connected to the battery controller or whatever?

Also, is there a way to test the battery itself?
I tried measuring the leads inside the laptop, that the battery connects to, and can only get 3.5-4V on some of the pins. Should that be higher, or is that the normal charging voltage?