Generator warning light

[Pat]

I own a 1998 S70 and for last few months my generator warning light has come on. For a little while the warning would come on and then it would go off. Now it stays on a lot longer and I notice the light comes on when I'm accelerating.

My husband thinks its the charger or battery - easy fix. I think its something more serious, any comments? Has anyone else experienced this problem? and did you fix it?