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Features Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 17 Sep 2002 11:12:19
In Reply to: Proper voltage of battery?, SAAB 9000 AERO, Mon, 16 Sep 2002 16:06:13 Members do not see ads below this line. - Help Keep This Site Online - Signup |
When you FIRST start the car, the 9000 EDU has a 'feature' where it shows the cranking voltage of the battery. It will hold this voltage until you hit the INFO button, or drive a few yards. The purpose of this reading is to give you an indication of the health of the battery.
The absolute voltage, within a range, doesn't matter much here. It's the trend. If you see the cranking voltage drop over a period of weeks/months, then it's a sign the battery is on the way out. The absolute voltage varies from car to car. I have a '92 that shows in the high 8 volt range with a brand new battery - until it hits 8.1 regularly for a couple of weeks do I think the battery needs replacement. And that's accompanied by very slow cranking. I have an '88 which shows 9.7 volts, and if it drops below 9.3, the battery is dead. That's a full volt different than the other car.
If your engine is cranking fine, then don't sweat the startup voltage much.
The real question is what is the voltage once you're underway. And that's more alternator than battery. Driving down the road on a cool morning, you should see in the 13 volt range, preferably above 13.4 or so. It may drop down to 13.0 or 12.9 stopped at a light, idling, with brake lights and blower on. On a hot afternoon, the voltage may be 0.5 volts or more lower. Why? Because the voltage regulator adjusts the output voltage as a function of heat - the hotter it is under hood, the lower the output voltage. So it may pump out 13.7 on a cool morning, but drop down to 13.0 stuck in traffic on a sweltering day.
If you want to know the health of your battery, get a decent voltmeter and a battery hydrometer. The hydrometer is a rubber bulb and a plastic body, and it measures the specific gravity of the electrolyte in each cell of the battery. Fancy words, but easy to use. Just open each cell in turn, and suck up some acid into the body of the hydrometer. A little needle will tell you the state of charge. Use the voltmeter to measure battery voltage and compare it against the EDU reading. I've seen EDUs off by 0.3 or more volts. It's an indicator, not a precision instrument.
As KeithG says, you should see about 12.5 volts or so on a good charged battery with the car off.
But if the engine is cranking quickly, the lights don't dim when you step on the brakes, then the battery is probably fine.
Good luck!
posted by 192.249.4...
, Tue, 17 Sep 2002 11:12:19 <-- Viewing This Message
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