Acer Aspire 2000 Cannot run with Battery connected?

My Acer Aspire shows the charging light when a battery is in and connected to the mains, it will power up but 5 seconds into the boot, it will just power down. The laptop will work fine on the mains alone.

I have tried 2 other batteries that I purchased thinking it was the battery but the same problem happens here.

If I run it off the mains and after the boot I put in the battery this will make the laptop power down after 5 seconds also.

Does anyone know if this is a BIOS section or isit a hardware fault?

Any ideas would be greatly accepted.