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Re: Low voltage reading; what does it mean Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Fri, 3 Jan 2003 12:52:30 In Reply to: Low voltage reading; what does it mean, John Levin, Fri, 3 Jan 2003 11:38:41 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The 9000 defaults to startup voltage as an indicator of battery condition. It's nice, but seems to cause significant worry.
The indicated startup voltage is useful as a TRENDING tool, and isn't that great for a pass/fail decision. That's because a 'good' startup voltage and 'bad' varies from car to car. I have a '92 that shows low to mid 9 volt range with a brand new battery, and only shows a poor battery when the voltage drops into the 8's. I have an '88 that shows 11 volts even with a 4-year old battery - anything below 10.0 volts is damn near a no-start condition. Since you have no history with the car, it'll take a while to learn it.
Battery voltage aside, how fast does it crank? If it seems slow to crank, that's more of a sign of a poor battery (or poor connections AT the battery) than the voltage. If the battery is original, I'd be suspect, as it's getting long in the tooth.
As to headlight brightness, when the engine is running, the electrical power needs of the car are supplied by the alternator, not the battery. If you're seeing over 13.0 volts (typically 13.3 to 14.1) while driving, then the alternator is doing its job. If you're seeing dips while driving, the voltage regulator may be getting tired. There are some transient high current requirements (AC compressor kicking in, etc) that can cause momentary brightness changes.
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