Laptop not working on battery power

I have an HP Compaq nc6400 running Windows 7.  The battery shows Fully Charged (100%).  When I try to use it without the AC power it runs for less than a minute and shuts down. 

I did find the Power Options and changed the Critical Battery Level and Low Battery Level.  They were 98 and 99 percent respectively.  I changed them to 10 and 20 percent respectively but that did not have any affect. 

In Devices, Battery -  I had two Microsoft ACPI-Compliant Control Method Battery entries.  Something I read told me there would be three entries under Batteries, one of them the Microsoft ACPI-Compliant Control Method Battery.  I uninstalled both of them.  When I restarted the computer the two entries were back. 

I suspect the battery is shot and I don't have another to try.  I just want to know if there is anything else I can try before I buy another battery.  It just puzzles me that it shows 100% rather than a red x through the battery.

Thanks for your help

No way to borrow one from a local computer shop/store?  And, test right there in the place?

Yeah I don't have a working relationship with anyone near me.  I was just hoping someone might be able to explain why it shows as a "100%".

Seems like if it turns out to not be the battery then I am obligated to let them fix it. 

Any more ideas on this?