Acceptable battery voltage
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Junior Member
Joined: Apr 2017
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2007 GL 450
Acceptable battery voltage
Hi all,
I'm still working through all the little Gremlins in my 07 GL 450. I've noticed that my battery only shows 12.38 volts when the car is off. It's not an old battery (Feb 16). I've also noticed that my power outlets don't function when the vehicle is off. The manual says they should, unless the car detects that the battery has too low voltage.
My question is what should the reading voltage be? What is a good battery type you've had success with?
Thanks for your time!
I'm still working through all the little Gremlins in my 07 GL 450. I've noticed that my battery only shows 12.38 volts when the car is off. It's not an old battery (Feb 16). I've also noticed that my power outlets don't function when the vehicle is off. The manual says they should, unless the car detects that the battery has too low voltage.
My question is what should the reading voltage be? What is a good battery type you've had success with?
Thanks for your time!
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Joined: May 2015
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From: Allentown, PA
'08 GL 320 CDI
Is that 12.4V immediately after you turn the engine off? If not, turn the engine off... turn your lights on for a minute or so... shut everything down... come back in an hour and check V again (before starting engine). How old is the battery? Does the engine crank fast? What is the V with the engine running?
Thread Starter
Junior Member
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2007 GL 450
DennisG01,
Thanks those are all questions I should have answered before! The voltage immediately after the engine stops is 12.4. The engine running gets the voltage to 13.7 (which is good I think), so I think the alternator is doing its job. The battery is marked as a AutoCraft Silver or Gold (can't remember) February 2016. This is the battery that came with the car when I bought it in January, so I'm not sure how it was treated before I got it.
The car cranks normally when cold and sometimes noticeably slower when warm. I did have the battery tested at Advanced Auto Parts and their tester claimed the battery was good, but I'm not sure what the power requirements of a GL are. I assume that they require very precise voltage to function just right.
Any thoughts? Thanks again for the reply!
Thanks those are all questions I should have answered before! The voltage immediately after the engine stops is 12.4. The engine running gets the voltage to 13.7 (which is good I think), so I think the alternator is doing its job. The battery is marked as a AutoCraft Silver or Gold (can't remember) February 2016. This is the battery that came with the car when I bought it in January, so I'm not sure how it was treated before I got it.
The car cranks normally when cold and sometimes noticeably slower when warm. I did have the battery tested at Advanced Auto Parts and their tester claimed the battery was good, but I'm not sure what the power requirements of a GL are. I assume that they require very precise voltage to function just right.
Any thoughts? Thanks again for the reply!
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Joined: Sep 2005
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From: s.f. bay area
s500 GL450 GL63 Z71XL Yukon 67 396 SS velle 68 Vert Camaro 69 RSSS Vert Camaro 75 Blazer
What dennis said is a good rough way to gauge a battery. You also mention advanced auto did a test. I'm assuming they did a load test. If they said it is good, your battery should be good as the measurements are indications for a good 12v battery. (you mentioned "only 12.38 volts" but that is what a 12v battery should measure when not charging or being drained)
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Junior Member
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2007 GL 450
I had always thought that a non-charging battery in good condition was supposed to hold at 12.6 volts. A quick search online suggests that at about 12.4 volts a battery is only 75% charged. Since the battery in it isn't necessarily the best one in the world, I'm not sure if that's causing the slow crank when the engine is warm or the lack of power outlets functioning when the vehicle is off. The manual says that the power outlets will work when the car is off (minus the cigar lighter), except when the battery voltage is too low. I guess my question is what is that cutoff voltage for outlets to turn off? And could this also be causing the slow warm engine crank?
