Chonic Alternator Failure

RedFish said
I've seen bad batteries show 12 volts. Turn the key and it drops like a hammer, 2 or 3 volts. Bad battery. A battery that properly stores cranking amps , at 70 degrees, no less than 9.5 volts after 20 seconds. Yes you would need to pull the coil wire to run this test. 20 seconds continuous run isn't going to hurt a good OEM starter. I don't know if 20 seconds or longer would damage a modern mini starter.
Since you've seen your battery drop to the 10s in a short period, I suspect it's going bad.
The general term "bad battery" covers a few different symptoms/conditions and creates different charging system conditions.
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Last few conventional batteries I had fit this description....would show 12 volts no matter how long it sat...put a load on it and down to 3-4 volts.....would suggest a load test, either as described above or by a tester....I am hooked on AGM batteries. Sure, they are a bit pricey. But if you give it good, clean cables/ends/lugs and have a functioning charging system they will last quite a while....with no need to clean the posts or add fluid....and no more staining concrete whenever you park...