Car battery losing its charge

[Jeff M]

Good afternoon, I have a 2 year old car battery (AGM 760 CCA) in a 2022 Hyundai that constantly "seems" to lose its charge. I'll check the battery during the day and, as an example, it will show 40% charge (12.2 volts). I put the trickle charger on it, and within about 15-20 minutes, the charger will show the battery is at 100 % (which is weird since the battery can't possibly charge that fast). I'll put a battery tester on it, get the same 100% reading and 13+ volts. Next day, down to 40% again. My 1st thought was parasitic drain, but if the car sits for 3-4 days during the winter (New York), the battery will show 25-30% charge and starts right up with no issues. I would think that a parasitic drain that drained the battery to 40% after 1 day would completely drain the battery after 3-4 days.
The above scenario has been ongoing for months now-battery seems to lose its charge, trickle charge for 15 minutes, battery seems to be at 100% then loses charge again. After driving for a couple of hours the battery will show about 75% charge, yet next day is at 40%. The battery never drains completely and always starts immediately even in cold weather.
I've done a load test and a cranking test and both are fine.
I've also used a 2nd battery tester and a multimeter to verify that my original battery tester is working fine (they provide a similar reading).
If anyone has any thoughts, I will certainly appreciate your input. This is really perplexing to me. I don't want to buy a new battery if I don't need to but it's hard to tell if this battery is good or not.
Thanks a lot for any help.

 

[narkedatninety]

Do you have another battery you can try? It would probably be the quickest and easiest way to ascertain whether the problem is with the alternator circuit or the battery itself.

 

[EricMark]

I have found it takes a long time to fully recharge a lead acid battery be it flooded, or AGM (VRLA) it takes time to convert the sulphur back into sulphuric acid.

`The first time I was able to experiment with time was on finding two small 7 Ah batteries from a stair lift, I knew the history the stair lift had been unplugged, stuck halfway up the stairs, and it had no hand crank option so had to fit two new batteries and old ones got lost for around 6 months. So normally I would have considered them as dead.

I could not charge the battery with a smart charger, as they would not work under 7.8 volts, it would see it as a 6 volt battery, so wired in parallel to a known good battery. And put pair on charge plugging the charger into an energy monitor so I could see what was going on.

It sat there for nearly two weeks before it started to charge, and then it was as if some one had flicked a switch, and it fully recharged. This was repeated with other battery of the pair, and has been done many times since.

So the smart charger will to start with work like any other stage charger, the one I had there were 5 stages, 3.8 amp, 3 amp, 0.8 amp, 0.1 amp and off. There was an option to select under or over 12 amp hour, and as used with the batteries reclaimed it would alternate between two charge rates depending on voltage, so would charge to 14.4 volt the switch to lower rate or off, until at 12.8 volt when it would switch back to the higher rate.

With a battery which has not failed it can take up to two weeks left on the charger to fully recover, and the in charger display does not tell you how the charging is going, it will always show fully charged. But it is slowly moving the sulphur back into the acid.

So being a three car family one tends just to sit there on charge for a week every so often to refresh the battery, in the old days of flooded batteries we could use a trickle charger and top up the cells after, but today the smart charger is the only way.

 

[Jeff M]

I have found it takes a long time to fully recharge a lead acid battery be it flooded, or AGM (VRLA) it takes time to convert the sulphur back into sulphuric acid.

`The first time I was able to experiment with time was on finding two small 7 Ah batteries from a stair lift, I knew the history the stair lift had been unplugged, stuck halfway up the stairs, and it had no hand crank option so had to fit two new batteries and old ones got lost for around 6 months. So normally I would have considered them as dead.

I could not charge the battery with a smart charger, as they would not work under 7.8 volts, it would see it as a 6 volt battery, so wired in parallel to a known good battery. And put pair on charge plugging the charger into an energy monitor so I could see what was going on.

It sat there for nearly two weeks before it started to charge, and then it was as if some one had flicked a switch, and it fully recharged. This was repeated with other battery of the pair, and has been done many times since.

So the smart charger will to start with work like any other stage charger, the one I had there were 5 stages, 3.8 amp, 3 amp, 0.8 amp, 0.1 amp and off. There was an option to select under or over 12 amp hour, and as used with the batteries reclaimed it would alternate between two charge rates depending on voltage, so would charge to 14.4 volt the switch to lower rate or off, until at 12.8 volt when it would switch back to the higher rate.

With a battery which has not failed it can take up to two weeks left on the charger to fully recover, and the in charger display does not tell you how the charging is going, it will always show fully charged. But it is slowly moving the sulphur back into the acid.

So being a three car family one tends just to sit there on charge for a week every so often to refresh the battery, in the old days of flooded batteries we could use a trickle charger and top up the cells after, but today the smart charger is the only way.

Thank you for your input.

 

[Jeff M]

Do you have another battery you can try? It would probably be the quickest and easiest way to ascertain whether the problem is with the alternator circuit or the battery itself.

Unfortunately I don't have access to a 2nd battery, thanks for the suggestion though.

 

[Rockingit]

OK, so - fully charge the battery to the best of your knowledge (anything over 13.3V, I'd suggest) and then disconnect the neutral from the vehicle for a couple of days. Yes, it'll make your immobiliser and alarm go skits and you'll have to reset the clock... but what it WILL do is eliminate whether it's the vehicle causing the problem or just, as I suspect, a faulty battery.

 

[DPG]

I have an issue on my Jag XF which is similar. Sometimes the battery brains over a a couple of days - Sometimes it can last for over a week and still be at 90%. I've narrowed it down to parasitic drain, but unfortunately it's intermittent. The car shuts down in 4 or 5 stages and you can see the current dropping at each stage. By the time it is fully shut down it should be drawing less than 50mA, but occasionally something stays awake and it sits there at 1.7A.

I suppose my point is don't rule out parasitic drain after taking measurements once or twice. It took me a long time to realise what was going on.

The problem is the car can sit without use for a few days. If it was in daily, or even just every 2 or 3 days use then to be honest you wouldn't even know it.had a problem.

I just need to find out what it is now!

 

[mainline]

Good afternoon, I have a 2 year old car battery (AGM 760 CCA) in a 2022 Hyundai that constantly "seems" to lose its charge. I'll check the battery during the day and, as an example, it will show 40% charge (12.2 volts). I put the trickle charger on it, and within about 15-20 minutes, the charger will show the battery is at 100 % (which is weird since the battery can't possibly charge that fast). I'll put a battery tester on it, get the same 100% reading and 13+ volts. Next day, down to 40% again. My 1st thought was parasitic drain, but if the car sits for 3-4 days during the winter (New York), the battery will show 25-30% charge and starts right up with no issues. I would think that a parasitic drain that drained the battery to 40% after 1 day would completely drain the battery after 3-4 days.
The above scenario has been ongoing for months now-battery seems to lose its charge, trickle charge for 15 minutes, battery seems to be at 100% then loses charge again. After driving for a couple of hours the battery will show about 75% charge, yet next day is at 40%. The battery never drains completely and always starts immediately even in cold weather.
I've done a load test and a cranking test and both are fine.
I've also used a 2nd battery tester and a multimeter to verify that my original battery tester is working fine (they provide a similar reading).
If anyone has any thoughts, I will certainly appreciate your input. This is really perplexing to me. I don't want to buy a new battery if I don't need to but it's hard to tell if this battery is good or not.
Thanks a lot for any help.

What sort of battery tester are you using.

 

[James]

You say it can be left in the cold for a few days and although your tester is showing low battery, the car starts fine.

I suspect that you are trying to find a problem that is not there.

battery charge level meters are notoriously unreliable for lead acid batteries, if it is cranking over and starting normally then the battery is fine.

 

[Jeff M]

What sort of battery tester are you using.

I am using a Solar BA9tester

 

[mainline]

I am using a Solar BA9tester

It should give fairly accurate results.

Bear in mind your car will probably have a smart charging system, so worth having a read up on those.