Originally Posted by
dedwards0323
Looks like you are using a battery tester like
THESE, which is good for determining overall battery condition. I would tend to agree with those that point to an alternator issue. A functional failure with the alternator has surfaced. The functional failure being defined as "inability to adequately provide/sustain charging capability to the electrical system". That failure mode could be caused by a number of faults, One could be simply a slipping belt condition, which is easily fixed. Take a close look at the drive belt to see if you see any signs of fatigue (stress cracks along the webbing). Change the belt if you finds this failure mode. Most direct alternator failures are addressed by a new alternator; rebuilt parts industry has made this somewhat economical to us DIYers. . You could remove the alternator & have it checked by a service shop that specializes in alternator & starter rebuilds. These shops have the capability to check the alternator under load. I've got one near to me that I've used occasionally. Good luck with your ongoing diagnosis & repair.
I would not expect the belt to slip because of the belt tensioner. Oil or water/coolant could cause it slip. Check the belt condition anyway. You have to sure that you have the correct amperage as well as voltage. The correct voltage must have sufficient amperage to start the car.
A loose or poor battery/ground connector will allow the voltage to show but will fail the amperage requirements. Corrosion in the battery cables means there are acid vapours leaking from the battery at the terminals, get a new battery. The old pitch batteries leaked at the posts all the time and we used to put those acid eating washers around the posts, the new polypropylene batteries should not leak as the plastic shrinks around the post as the plastic cools, if you have leakage at the post you must get a new battery or the acid will start to eat your car.
Those pitch batteries slowly lost power if left on concrete etc as the charge leaked through the slightly conductive pitch, the new plastic batteries do not discharge through the plastic.