Battery Gauge Question
Thread Starter
Instructor
Joined: Jul 2014
Posts: 135
Likes: 17
From: Punta Gorda, Florida
Battery Gauge Question
I took my ‘64 roadster out for a ride today and saw the battery gauge nearly at the -40 position. At idle it showed negative of zero. I’m not sure what a Battery gauge measures, but I’ve never seen it show that low. Usually it shows slightly negative and usually returns zero. The car was running normally and there was no indication of anything hot, no burning wire oder, nothing out of the ordinary. Any ideas out there?
Burning Brakes
Joined: Aug 2021
Posts: 807
Likes: 199
From: NH
Check the output of your alternator. It is probably 0. Check your battery, it is probably low now. Your ammeter is showing that you are removing energy from your battery (-#) rather than charging your battery (+#). If you continue to drive this way, you will kill the battery.
Last edited by dmtparker; Mar 18, 2022 at 08:40 AM. Reason: wrong question
Race Director
Joined: Apr 2005
Posts: 10,179
Likes: 2,306
From: Wesley Chapel, FL Las Vegas, NV
The battery gauge is an ammeter. It measures current flow in amps. Negative is current flowing out of the battery. Positive is current flowing into the battery.
When starting the engine or turning the lights on without the engine running you will see negative flow, that is power coming out of the battery. When the engine is running the gauge should show positive current flowing into the battery, in amps, and will slowly go toward zero as the battery reaches maximum charge.
Obviously, if the charging system is charging less, showing negative, than needed to create positive flow into the battery it will eventually drain the battery.
Three things to check.
#1 Battery - Maybe bad and won't take a charge or corroded battery connections
#2 Alternator - Output running should be around 14v
#3 If Alt voltage is ok check the voltage regulator
When starting the engine or turning the lights on without the engine running you will see negative flow, that is power coming out of the battery. When the engine is running the gauge should show positive current flowing into the battery, in amps, and will slowly go toward zero as the battery reaches maximum charge.
Obviously, if the charging system is charging less, showing negative, than needed to create positive flow into the battery it will eventually drain the battery.
Three things to check.
#1 Battery - Maybe bad and won't take a charge or corroded battery connections
#2 Alternator - Output running should be around 14v
#3 If Alt voltage is ok check the voltage regulator
