Hey - I'm a newbie to Forums

- but hopefully I can get some help.
I have a 95 C-280. The Battery Light came on along with ABS and Brakes - but then the lights went off. Like an Idiot I checked my Brake sensor - and it was good to go. Suspecting the Battery - I read 12.3v static and 13.3 at idle. A Dealer rep suggested loose wiring so I checked. All good but the Battery check again read 3v (left the trunk open overnight!) Enough - I changed the Battery. All OK for a few minutes - but I can faintly see the Battery Light remaining On.
Alterantor? Voltage Regulator? I'm capable - but don't have the manuals. Suggestions?