If it was the belt slipping you would hear it. And you could test that by just revving in a parking spot.

I wouldnt think its the battery since the battery just starts the car and the alternator runs it as well as recharge that battery. Could in theory be a loose connecting if the engine was torqued and moved the cables but unlikely. The battery light only comes on when the alternator isnt putting out more than 12V's and other lights usually come on also since the modules are losing power (kinda like when your car stalls)

I'm leaning towards an alternator/voltage regulator. As the load and speed increased the alternator couldnt keep up. Unfortunatly no place will diagnose that for free and just swapping parts is expensive. Your best bet is to get it diagnosed and replace the right part the first time.

 

I tested the battery and alternator and got 14v on both so I don't think it's the alternator... I am going to clean the grounds and tighten everything up on Friday and see if that does anything before I buy anything.... Might do the belts and a/c idler pulley(I can hear it "hissing") also just to eliminate that as a culprit.

 

You tested the alternator at idle but did you do a full field/load test on the alternator? It could be fine while just idling/cruising but with stress it fails. Just an idea.

 

From what I hear from my co-workers, if there is a problem with the alternator, it will completely crap out. If you do live near carlsen subaru, I can most likely have you bring your car in when I get off work and I can test it for you.

 

When my brake fluid was low, it would trigger the ebrake light under acceleration and it would turn off under braking when the fluid (presumably) would move forward.

 

Brake light and battery light together?