Weak battery question
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Tuned
Joined: Aug 2015
Posts: 396
Likes: 2
Weak battery question
So I am suspect of my batteries in my truck, they are 2 yrs old this November. When the truck sits over night its slower to crank over, but when it sits for a few days it's even worse. Starter is fairly new. I dont think it's a starter issue, because once the truck has started for the first time of the day and run a bit it turns over pretty quick. My connections look clean with no corrosion, these are Walmart maxx group 65 batteries, that are still under warranty. I just checked the voltage after sitting overnight and both batteries are showing a 12 to 12.6volts. Is that normal? Can they still test ok and still be weak?
Lead Driver
Joined: Mar 2006
Posts: 5,096
Likes: 1,498
From: western SD
A fully charged battery should read at least 12.5 volts. That said, the true test is a load test. A bad battery can show over 12 volts, and will fail a load test. When testing batteries, they should be tested individually.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Have you charged them up? Parallel battery setups tend to get mismatched over time, esp. with short trips and stop and go type driving. A load-test is only valid with a fully charged battery. This is 12.80 volts at 77° F for a sealed "maintenance free" battery. Once they get depleted the alternator will never get them back up too easily. They can check for defects like shorted cells or other problems with a hand held conductance type tester. But a carbon pile load test is still the best. They take a long time because they need to be charged up first (if weak) before the test and then again after the test, because it puts it through the wringer.
You can measure voltage across the terminals during engine cranking as kind of a "poor man's" load test. A defective battery is one that drops to 9.6 volts or less. In cold weather it might be a little lower, but a healthy battery will stay well above that in any case. A defective battery will often measure OK or reasonable with just a voltmeter across the terminals, and then choke whenever a load is put on it.
You can measure voltage across the terminals during engine cranking as kind of a "poor man's" load test. A defective battery is one that drops to 9.6 volts or less. In cold weather it might be a little lower, but a healthy battery will stay well above that in any case. A defective battery will often measure OK or reasonable with just a voltmeter across the terminals, and then choke whenever a load is put on it.
Lead Driver
Joined: Apr 2016
Posts: 7,170
Likes: 1,331
From: Bahstun
your GPs are a great load test
You should be able to get several GP cycles and still start up
did you remove a ground to a battery befor voltage test? 12 and 12.6 isn't good. batteries will fight if at an uneven voltage and also tells me your cables do have some corrosion if they were not equal.
You should be able to get several GP cycles and still start up
did you remove a ground to a battery befor voltage test? 12 and 12.6 isn't good. batteries will fight if at an uneven voltage and also tells me your cables do have some corrosion if they were not equal.
Postmaster
Joined: Sep 2007
Posts: 4,195
Likes: 6
From: Medford Oregon
I agree, load test is the only way to go. On my 99 it would barely turn over fast enough to start if I waited 2 or 3 days. Charge them up and it started quickly until the next wait. Voltages looked good when running though. Took it to a regional known service center and drivers side battery was at 80% and passenger side was at 20% on the load test. Original batteries were two years old from previous owner at 650 CCA. Interesting their computer indicated this was the correct battery for the truck. Told the shop to replace both with the 850 CCA and have not had a problem since. Then, once, I had to go out of town for almost 1.5 months and had to charge them as it just would not crank fast enough to fire the truck up. . .
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Fleet Mechanic
Joined: Aug 2013
Posts: 1,691
Likes: 2
From: Fallon NV
I'm doing this right now. Good info. mine show 12.48 at charge. They have sat 2 days now in connected. I need to go check them. At 3 days my truck will not fire off , just smoke and shudder.
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Mountain Pass
Joined: May 2017
Posts: 152
Likes: 3
From: Colorado
Last week i had a battery post go bad on my primary battery. Seems popular for people yo wedge a screw next to the post when the connector is broken or worn to make it tighter...i just threw in a battery from my 58 f100 which is severely undersized, which has made it crank a bit slower. Not sure if its related, but my radio is dead when i start the truck, id i pull the fuse in the radio and reinstall it, it comes on. Computer dropping out radio because of low CCA?
make sure the stronger battery is on the passenger side,
make sure the stronger battery is on the passenger side,
Lead Driver
Joined: Apr 2016
Posts: 7,170
Likes: 1,331
From: Bahstun
some radios dont have a big battery for memory and once you drop below 9v, it will reset after a few seconds while cranking with GPs on
mismatched batteries will result in the new one being drained by the bad one
mismatched batteries will result in the new one being drained by the bad one
Tuned
Joined: Feb 2008
Posts: 445
Likes: 1
From: Forest Grove, BC
Im having same issues with my wood truck, 94 f250 with a 95 PSD Was not starting after sitting a few days. I determined that one of my batts was pooched. They are both 850cca batts. Since its only used for wood in summer and moving sled around in winter I can't justify spending $350 on batts right now. I do have 3 brand new deep cycles sitting in my shop. two 27 series and one 31 series 12V. Im gona put in the 27's under the hood and the 31 in the back hooked up through a solenoid for when I have my camper on. They are lower in CCA's but with all three in parallel, they should be more then good enough to turn her over. Heres Hoping lol
Lead Driver
Joined: Sep 2002
Posts: 9,473
Likes: 2,009
From: North Texas
I did find out from a pal in MD his local Walmart has 850CCA batts, while mine in TX does not...at least neither the DFW nor Hou locations.
Be sure to read Knotty's thread about battery cables and whatnot. Worth the hassle to clean them all and see if it helps.
Be sure to read Knotty's thread about battery cables and whatnot. Worth the hassle to clean them all and see if it helps.
Lead Driver
Joined: Apr 2016
Posts: 7,170
Likes: 1,331
From: Bahstun
