Battery Test Question
Thread Starter
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Senior User
Joined: Mar 2003
Posts: 466
Likes: 1
I agree that 4 years in Las Vegas heat is pushing it. So, now I have two new batteries and the voltage while driving is 13.0 to 13.3. I will see how this goes. Since I have a digital voltage readout I can keep a close eye on it all the time.
Cargo Master
Joined: Feb 2008
Posts: 2,862
Likes: 44
From: Tooele, UT
ok here is why your meter dropped to 10V when you started it. when you initially start your truck it draws all it's power from your battery. as soon as the engine is running it switches over to the alternators power. the alternator will replenish the battery power that was lost at start up and then continue to run everything electrical in your truck. even though your voltage is a little lower than normal it still isn't low enough to really worry about. once it starts dropping below 12.8 is when you have an issue. also when your voltage didn't change after you turned the a/c on that is a good thing and means that your alternator is still able to hold a load. if it was really bad then it would have dropped considerably.
i am with you on changing the batteries now though. i really hate to be stranded. i am actually going to be changing mine out here very shortly even though they are still working good.
the duralast gold tops at autozone are an excellent battery plus they come with an 8 year warranty. if anything goes wrong with them you take them back to autozone and replace them with no questions asked.
i am with you on changing the batteries now though. i really hate to be stranded. i am actually going to be changing mine out here very shortly even though they are still working good.
the duralast gold tops at autozone are an excellent battery plus they come with an 8 year warranty. if anything goes wrong with them you take them back to autozone and replace them with no questions asked.
Thread Starter
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Senior User
Joined: Mar 2003
Posts: 466
Likes: 1
mxer0022, thanks for the reply. I am not worried about the drop to 10 during start. Before I replaced the batteries my running voltage was low 12 to high 12. Since replacing the batteries it is staying at 13 to 13.3. About 6 months ago it would be around 14.
Can an alternator slowly go bad? If so then I will just upgrade when I get some more cash.
Can an alternator slowly go bad? If so then I will just upgrade when I get some more cash.
Posting Guru
Joined: Dec 2006
Posts: 1,078
Likes: 0
From: Kansas City/Breckenridge
mxer0022, thanks for the reply. I am not worried about the drop to 10 during start. Before I replaced the batteries my running voltage was low 12 to high 12. Since replacing the batteries it is staying at 13 to 13.3. About 6 months ago it would be around 14.
Can an alternator slowly go bad? If so then I will just upgrade when I get some more cash.
Can an alternator slowly go bad? If so then I will just upgrade when I get some more cash.
Lead Driver
Joined: Jul 2007
Posts: 7,868
Likes: 9
From: Rhode Island
ok here is why your meter dropped to 10V when you started it. when you initially start your truck it draws all it's power from your battery. as soon as the engine is running it switches over to the alternators power. the alternator will replenish the battery power that was lost at start up and then continue to run everything electrical in your truck. even though your voltage is a little lower than normal it still isn't low enough to really worry about. once it starts dropping below 12.8 is when you have an issue. also when your voltage didn't change after you turned the a/c on that is a good thing and means that your alternator is still able to hold a load. if it was really bad then it would have dropped considerably.
i am with you on changing the batteries now though. i really hate to be stranded. i am actually going to be changing mine out here very shortly even though they are still working good.
the duralast gold tops at autozone are an excellent battery plus they come with an 8 year warranty. if anything goes wrong with them you take them back to autozone and replace them with no questions asked.
i am with you on changing the batteries now though. i really hate to be stranded. i am actually going to be changing mine out here very shortly even though they are still working good.
the duralast gold tops at autozone are an excellent battery plus they come with an 8 year warranty. if anything goes wrong with them you take them back to autozone and replace them with no questions asked.
Also, if you are down into the 12s, be it 12.8-12.9, you will slowly kill your batteries. Ideally you'd want at least 13.4-13.6, with 14.4 being perfect.
As far as the Duralast batteries, I heard they are made by Johnson Controls - the same people who make Optima batteries.
Cargo Master
Joined: Feb 2008
Posts: 2,862
Likes: 44
From: Tooele, UT
i work at autozone part time, military pay isn't the greatest...haha, and i have never had someone bring in a battery and had the warranty denied. 8 years is a long time and knowing that i wouldn't have to buy any batteries is a nice piece of mind. especially two.
Cargo Master
Joined: Dec 2007
Posts: 2,196
Likes: 120
From: Carstairs Alberta
if you test both batteries together essentially you are testing 1 REALLY big battery. therefore the load for the test should be twice as large.yes you replace them in pairs even if only 1 has failed. however they must be tested separately to get get an accurate test. you just replaced both batteries and yet your voltage is still down, take a good multimeter and check voltage at the battery posts, not on the clamps.(every connection has a small voltage drop)if a diode is weak the alternator will be able to produce full vlotage as long as the amp load is low but as load increases its ability to maintain full volts is hindered. with the use of a good battery/alternator tester you can load test the alt and see if it can produce spec amperage. Lost wages huh lots of grit in the air to grind up alternator brushes and commutators,lots of heat to stress connections inside the alt,which can cause high resistance which reduce output. my opinion is that even with a dead or no batt at all you will show full volts when running, so if volts are down look at alt first. not a master but i have worked around 12/24 truck for about 20 years now. i have had lots of guys tell me they HAD to have all new batts, abut they passed load test perfectly, cleaned posts a couple new cable ends soldiered on and it started like a million bucks
