Car battery question

This place is filled with dentists and Macguyvers so here is a question about car batteries. Picking up a beater car that has sat for about 4 months and battery is dead. It's only about 2 years old and curious if there is a magic number that it should read to indicate that it will charge up ? I was able to jump start it after letting it sit about 4 minutes and after 10-15 minute drive it was still not able to crank without a jump. I did not geta battery light indicating alternator issues and I was assuming it was working since the car drive fine after the jump. I didn't have a meter with me to check to see if it had proper output, I'll have a grave full of harbor freight and Craigslist tools at my disposal when I get it home tonight.

I think you have to load test a battery to really know which most people doent have, but if it still needed a jump after running for 10 minutes it sounds FUBARED

when you do shut it down it make sure you got it pointed it in a direction so you can get at the battery to easily do a jump

sealed or unsealed battery? If sealed I would think fine. I have had cars and boats sit longer than 4 months and be fine. I would put a trickle charger on it overnight and top fluids if un-sealed.

If the battery was dead and it froze it is done. Batteries are cheap in the big scheme of car ownership. Get a new battery.

Yes, there are magic numbers. Do you have a charger and a multimeter? If so, charge it overnight and then check the voltage. Let battery sit for an hour or so and test again. A fully charged flooded lead-acid battery should test >12.4 immediately after disconnecting charger. If it reads <12.2 immediately after disconnecting charger, your battery is getting old and tired, and should be replaced. If it reads <11.8v immediately after disconnecting charger, it may have a bad cell. Battery voltage will read high the first hour or so after you disconnect the charger. After a couple hours an okay battery may test as low as 12.0v. The above assumes temps >50F.

Always test with an open circuit, i.e., pull the battery out of the car or disconnect the negative cable. When diagnosing, it's best to charge with an open circuit because it's possible that you have a current leak that prevents proper charging.

ETA: An auto parts store can perform a better diagnosis with more advanced tester.

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Originally Posted by fatnslow

This place is filled with dentists and Macguyvers so here is a question about car batteries. Picking up a beater car that has sat for about 4 months and battery is dead. It's only about 2 years old and curious if there is a magic number that it should read to indicate that it will charge up ? I was able to jump start it after letting it sit about 4 minutes and after 10-15 minute drive it was still not able to crank without a jump. I did not geta battery light indicating alternator issues and I was assuming it was working since the car drive fine after the jump. I didn't have a meter with me to check to see if it had proper output, I'll have a grave full of harbor freight and Craigslist tools at my disposal when I get it home tonight.

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You have to drive 9 minutes after one start to fully recharge the battery. To fully charge a dead battery, you'd have to drive for 12+ hours. And what Steve said. You can get geeky and buy a specific gravity tester and check each cell too. Most auto parts will do a free load test.

The biggest factor is what brand and what CCA is the battery. I like JCI batteries, and at least 500CCA

a HD mechanic told me the best way to find a good battery is pick it up, if it weighs lots its better than a battery that is light

that and its gona be 50$ for the 1/4 oz

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Originally Posted by k2skier112

You have to drive 9 minutes after one start to fully recharge the battery. To fully charge a dead battery, you'd have to drive for 12+ hours. And what Steve said. You can get geeky and buy a specific gravity tester and check each cell too. Most auto parts will do a free load test.

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True but a good battery will restart a warm car engine after only a couple three minutes usually in my experience. If you let it sit for a while and try to start a cold engine you are going nowhere of course because of the factors you mention.

"A 100 percent fully charged battery will not freeze until approximately minus 76 degrees Fahrenheit. A fully discharged battery can freeze at or around 32 degrees,” Kimbrough said in a telephone interview. The difference between a fully charged and discharged 12-volt battery is not that big.Feb 18, 2014"

Also if it is made Exide it was garbage when new. Johnson Controls is way better among the two most common manufacturers used by most America battery brands.

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Originally Posted by XXX-er

a HD mechanic told me the best way to find a good battery is pick it up, if it weighs lots its better than a battery that is light

that and its gona be 50$ for the 1/4 oz

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A dead battery weighs the same as a new battery.

To the OP - if it holds a charge, after being charged on a standalone charger, then you might be OK. If it doesn't, time for a new one.

I like Costco for batteries. Good prices, great warranty. They sell Interstate brand now, which I'm sure are just Johnson Controls or Exide anyway, as there just aren't many battery manufacturers anyway.

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Originally Posted by GeezerSteve

Yes, there are magic numbers. Do you have a charger and a multimeter? If so, charge it overnight and then check the voltage. Let battery sit for an hour or so and test again. A fully charged flooded lead-acid battery should test >12.4 immediately after disconnecting charger. If it reads <12.2 immediately after disconnecting charger, your battery is getting old and tired, and should be replaced. If it reads <12v after disconnecting charger, it likely has a bad cell and must be replaced. Battery voltage will read high the first hour or so after you disconnect the charger. After a couple hours an okay battery may test as low as 12.2v. The above assumes temps >50F.

Always test with an open circuit, i.e., pull the battery out of the car or disconnect the negative cable. When diagnosing, it's best to charge with an open circuit because it's possible that you have a current leak that prevents proper charging.

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this what I need.

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Originally Posted by El Chupacabra

A dead battery weighs the same as a new battery n.

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i think what Dudley meant was that after 40 years of changing batteries in his experiance a better performing battery will have more lead in it, more lead will weigh more, ergo a heavier battery will be a better battery

and 50 for 1/4 eh

Yep. Voltage doesn't measure a batteries ability to deliver starting amps. Just voltage. So no number is magical. I've had awesome voltage that completely goes away with a load.

As someone mentioned earlier, easy way is trickle charge for 24 hours. If it still doesn't work it is garbage.

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You either need a new battery or you don't,

I change mine when they start to die usually after about 7 years,
because i don't wana deal with a breakdown and it gets fucking cold up here
which kills the cranking power

on the TDi i had a battery blanket T'ed into the block warmer plug
cuz you really need that extra craking power on a diesel

I moved the blanket over to the ranger but i hardly ever even had to plug that truck in



or you have charging issues/ bad battery connections

$100 for a new battery is cheap peace of mind.

It takes a long time to charge a completely dead battery.

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Originally Posted by XXX-er

You either need a new battery or you don't

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Sometimes a battery may perform poorly due to sulfated plates but can be restored to like-new performance. Some people replace batteries that could have been restored with a few full charge/discharge cycles. OTOH, when the sulfation gets too bad, the battery may not be capable of restoration.

7 years between battery changes is a long time. You're doing something right.

JHFC people, the tester at the ORiley. Take it out and give them 2 hours to charge/test. OP got the same tool or better? Use it. It never failed me in saying batt was bad (strung it along but died) or “good” (last 1yr + and OK in 0f range).


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^ ^ ^ good advice for non-DIYers. Most shops have a load tester that takes only a few minutes.

My plan is to get it home and charge overnight then check voltage, try to start a few times and drive to a battery shop to have them load test it. I didn't know what the critical voltage reading is as for go/no go as a rule of thumb and didn't want to require a jump waiting for a bystander to help or do the AAA jump lotto during covid away from home.

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Originally Posted by fatnslow

My plan is to get it home and charge overnight then check voltage, try to start a few times and drive to a battery shop to have them load test it. I didn't know what the critical voltage reading is as for go/no go as a rule of thumb and didn't want to require a jump waiting for a bystander to help or do the AAA jump lotto during covid away from home.

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this doesn't help your immediate problem, but buy one of these (not necessarily this specific model) for the future: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

no waiting for anyone else to help. no worry about parking in such a way that another car can jump ya. bonus is that it can charge your phone when camping.

I was going to add that any good garage or auto parts stores have battery testers. They charge them and then determine the voltage even emulating a load many times. But if you do not want to spend money on a new battery (since these places also want to sell you their higher priced batteries) you could charge it disconnected from the auto, let it sit for a few hours test the voltage again. Stick it in the vehicle and connect it up, try starting it. If it starts, then let it sit over night and try starting again. If there is something electrically wrong with the vehicle it could be draining the battery, but the testing would tell you for sure if the battery is shot.

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Originally Posted by GeezerSteve

Sometimes a battery may perform poorly due to sulfated plates but can be restored to like-new performance. Some people replace batteries that could have been restored with a few full charge/discharge cycles. OTOH, when the sulfation gets too bad, the battery may not be capable of restoration.

7 years between battery changes is a long time. You're doing something right.

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I was stuck on Haida Gwai for 9 days waiting for the ferry so I hung out at the hostel where I met this extremely eclectic guy who owned the place, he told me as long as there are no dead cells you can buy a battery rejuvenator from china for 30 $ that will fix a battery , buddy was completely off the grid running his hostel on solar, he liked the big truck/tractor batteries he had salvaged from the dead battery core pallet at NAPA, he would be riding his electric scooter past NAPA if he seen a likely battery he would check it for any dead cells with his meter, if it was ok he would take it home & reuse it. He said a lot of the batteries were just dead from abuse by being overloaded with acessories so when equipment comes in for repair the batteries get replaced cuz the mechanic can charge more but there is nothing wrong with the battery

he told me the big killer in solar instals was running the batteries down too far, what happens is systems get designed dfown south and they work fine in summer but you get up narth in winter there is < 8hrs of shitty sunlight with the sun low on the hills so the batteries get comepletely run down and the system fails

he also said china is way ahead of us on solar, smart guy he was doing equations designing stuff in his head I listened to him carefuly for 7 days and could acertain no crazyness



Me I don't want to fuck with batteries or vehicals at -20 so if I need to jump a battery just once (usually in the winter at -20) I assume it on the way out so its a sign I should plug in the block heater./ battery warmer just to get me to spring cuz a warm engine with a warmed battery has way more cranking power

I have this Noco jump starter. It's the bomb. Holds charge forever and has built in voltmeter

https://www.batterymart.com/merchant..._1000x1000.jpg

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Originally Posted by XXX-er

a HD mechanic told me the best way to find a good battery is pick it up, if it weighs lots its better than a battery that is light

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You're thinking of cabbages.

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Originally Posted by bobz

You're thinking of cabbages.

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probably ^^ a good thing to know !!