Sony SR21K battery problem

[Martyuk39]

I've inherited the above laptop. The battery is at 0%. It is present in the system. I'm wondering if I should get a replacement battery - is it pretty much likely to be the battery at fault or could there be a fault with the system as a whole? It's been residing in a dumping ground in our warehouse for a couple of years and I recently un-earthed it. It's not very powerful but it's nice and light and would be handy to have around. Works fine on mains power apart from the battery issue.