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Discussion Starter · #1 · (Edited)
Ok, when I had my '95 Aero checked before I bought it the Saab Spec. Shop said it would need a new battery soon, since the readout on the dash was only reading 8 volts during start-up and right after then going to 13.5. But, I had the guys at a chain autoparts store do a LOAD TEST on the battery puting out 13.4 Volts, and check alternator output 14.8 Volts at IDLE, all came back GREAT?? So what gives should I not belive my dash readout? :eek:
 

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the guys at a chain autoparts store do a LOAD TEST on the battery puting out 13.4 Volts,
Load test should be with the engine stopped and should be reading approx 12volts. My car display doesn't register correct reading until car has started moving and reads 9.9 volts when started and stays at this figure until mobile.
 

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Discussion Starter · #3 ·
Mine does the same?

Ok, so it is OK for the car to read low voltages till it is mobile correct?:)
 

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The voltage readout that's low is the battery voltage measured during cranking. Around 10V is about as low as you'd want it to go but it's like anything else, if it's working ok and consistent, don't worry about it. :)

Might just want to check that the earth to the car body is sound.

David.
 

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Discussion Starter · #5 ·
He checked that.

When it was hooked up he had me start teh car and see how much the voltage drooped while cranking the car over. The tester said the battery was putoing out 11 volts while cranking while the readout on the dash said 8.5 volts????:evil:
 

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What you need to observe is a series of back to back dash display readings below 9 volts. Once in a while the dash display will display low voltages which are no problem. If the dash display consistently reads as low as that then the battery won't be long for this world.


The dash gauge is not precise and a full blown voltmeter on a battery tester able to test drawdown as well as static voltage will always be more reliable.

The dash display reads and holds the voltage AFTER the starter stops and the engine is running. The you need to move the car around 50 ft before the alternator output shows up.

14.8 is a tad high for the alternator output but not surprising if the battery has been drained a bit. My dash display reads 14.2 as a maximum. Alternator voltage depends a lot on load and engine speed and reacts to the battery voltage as well. Lowest readings on the volt meter will be with a fully charged battery and all electrical accessories running. Highest voltmeter reading will be with a partially discharged battery and little or no electrical loading.
 
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