Battery warning light when accelerating

I have a 97 manual toyota corolla with about 160,000 miles. The battery warning came on during a roadtrip. I was using the highbeams and running the heater on high. I stopped running the heater and highbeams. However, the light still keeps coming on. It only comes on when I accelerate and goes off when I apply the breaks. I took the car in to have the battery tested. I was told besides some coercion on the bolts the battery and alterantor were fine. The coercion was removed but the light still comes on.