The battery in my car has been though quite a lot since my car seems to drain it on it's own over about a 2 week period if it's sitting... it's also had a couple of times when I've left it on change for 2 or 3 days having forgotten that I've put it on. The battery is about 3 or 4 years old now - it's an Optima Red Top.

My alternator seems to be so stiff that the belt slips at times, and last night I noticed that it was slipping really badly and my voltage was reading about 12.8 instead of it's usual 13.8....

I think I need to replace the alternator, I was wondering if I should replace the battery at the same time....

How do I make the determination of which components to replace? I drove home (20 mi) last night from work with lights on and the voltage didn't sink at all from 12.8 or so. Do you think it's safe to drive (i.e. how long do you think I have before it breaks down)? Can I wait a bit to fix it and still drive it? Any diagnostics I should carry out?

BTW - this is a subaru alternator, but in a 914

I got a voicemail from my coworker saying that I had left my parking lights on yesterday and he turned them off for me....

I guess my belt tension is not quite sufficient and my battery was low because of the lights being on all day. It squealed like a stuck pig this morning when I started it, but after it got some grip the voltage went right back to 13.8.

Maybe it's not a problem at all - I'll tighten the belt a bit and see what happens.....

might not be either how about the voltage reg