Quote:
Originally Posted by unkl300d
...
A fully charged battery is supposed to float at some said volts. What is the margin of voltage loss just standing without cables attached??
|
No load, fully charged terminal voltage of a car battery should be 13.2V. You'll only see this for a short while after disconnecting the battery charger. With no load and time, it'll drop to about 12.8V give or take a few tenths of a volt. It should stay there for a very long time until you discharge it some.
12.55V seems a tad low for immediately taking off the charging circuit, but since battery cables were still connected, is probably OK (it sounds like you do still have some load running it down).
You should see ~14V at the battery terminals when the battery is charging. The battery cannot reach full charge until the applied voltage is >13.2V, and you need a little extra on top of that to push some current through it to make the chemical reaction of charging occur. Your readings all sound fine and I wouldn't consider them any problem without any other evidence (in other words, sounds like the alternator/regulator are probably A-OK).
Your declining battery voltage when disconnected seems the likely culprit. I wouldn't fuss over the .01V changes, but wouldn't expect to see 0.1V changes too fast. If it was this way when new, then I'd consider it defective. Test might be to connect a small light across it (e.g. glove compartment light) for a couple of hours. The battery voltage shouldn't dip too much with that small of a load (I'd expect 12V or better). I left my glove compartment open for ~9 hours in my gasser the other day and I didn't even notice the discharge on the battery when I went to start it. Felt like an idiot for doing it, but what can ya do?
All in all, it sounds like the new battery is not (no longer?) holding a charge. As I recall, you said you ran the new battery down pretty deeply. If so, try connecting a 3 Amp trickle charger to it for a few (2-5) days to see if it seems to recover. It is possible one cell is weak from the experience and can't hold much charge anymore. That'll cause the no-load voltage to drop faster and quicker than normal, and will cause that cell to not be able to keep up on the current demand when starting, so you won't get too many tries before there's not enough voltage left to crank over the starter, which is what you seemed to describe. A nice, slow, long trickle charge might get enough current through that cell to get it charged up and able to keep up with the other cells.
Also, check the water level in all six cells to see if they completely cover the plates. Running it down could affect the level, but it shouldn't affect it by enough to expose the plates. If they are exposed, it probably wasn't right when you got it.
BTW, I'd disconnect the battery when not driving until I found and fixed the discharge. As suggested, disconnect battery and put meter in series (or better, a small 12V test light). Pull fuses until meter reads ~0V (test light goes out). Start with known loads -- clock, dome light, etc. -- since you know they will be drawing some. Don't forget, not all circuits have fuses in the box and at least one (the starter itself) has none (but it does have a relay). Check a wiring diagram to make sure you've disconnected the battery from everything.