Car Battery on it's own with 14.3 volts is bad, I would also confirm volt meter is working, because 12volt car batteries can't generate 14+volts
You are correct car doesn't need an alternator to run, so with a good battery engine will start and drive , but only for 1/2 hour to and hour without head lights on, depends on batteries charge when you start.
New battery will have 12.8v = 100% life
12.4v = 75% life
Battery that's due to be replaced will have 12.2v and may not crank starter on cold morning
With engine running and good alternator voltage at the battery will be over 14volts just after starting, then will drop down to 13.6volts(approx.) to maintain battery's 12.x volts, that's the extra power the alternator puts out, the regulator keeps the voltage below 15volts and above 13.5volts
If your alternator failed it can take a battery with it, if you don't catch it in time.
Alternator can start putting out 15+volts all the time, this will "cook" the battery.
Or it can output 12.8v or lower and that will slowly discharge the battery.
Car batteries are made to quickly discharge amps(start an engine), then quickly recharge, long power drains kill them.
Deep Cycle batteries are made for long drains, but they don't start engines well, they do work just not well.
If you have someone to crank engine, put volt meter on battery.
Then have them crank the engine, voltage should not drop below 9.5volts
To do a proper load test unhook coil and crank engine for 15 seconds, voltage should not drop below 9.2volts.
Last edited by RonD; 01-10-2014 at 03:24 PM.