Battery, alternator or something else

[RustyPile]

Originally Posted by forestb

So at the battery I am getting 12.01 volts and the same at the post of the one wire alternator. My gauge is still reading around 11 volts. It might be off by a volt.

You didn't say whether the engine is running or not. 12 volts at the battery when the engine is running usually means the alternator is not charging. When checking a battery without the engine running, a fully charged battery will read 12.50 volts. Depending on the load being applied at the time of the test (electrical items turned on), a functioning alternator will produce 13.7 - 14.2 volts at the battery. The big wire on the back of the alternator is simply the other end of the positive battery cable, so the 2 points will always read very nearly the same voltage (+/- .1 - .2 volts), engine running or not. The 11 volt reading at the in dash voltmeter is probably correct and just represents a 1 volt drop over the length of the wire.

Based on what's happening now, I doubt the first battery was bad - just improperly tested.. A 30 minute "quick charge" will not build enough charge in a dead battery to give an accurate test.. 90% of the time, the battery will always test "bad".. A dead battery needs a slow charge for a few hours to bring it to full charge.. Never use the alternator to charge up a dead battery. Alternators aren't built to work like that.