Flat Car Battery Issues

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outdoorsnz

674 posts

Ultimate Geek

#319505 1-May-2025 11:49

I recently purchased this vehicle. Had for over a month or two.

Drove car fine on Sunday. Monday lunch time dead flat (around 7.5 V). Charged with 2amp slow charger and disconnect charger 5pm next day Tuesday. Hooked battery up (13 V) and started car to test all fine.

Wednesday battery dead flat (around 8 V). Repeated charging procedure so I could take it to local garage to test today Thursday.

Battery would be about 3 years old. Garage tested it and said it battery not faulty. Quite possible that it needs a decent charge so currently have it hooked up to a 4.7AMP charger (older one) to get battery fully charged.

We tested parasitic drain and no issues there. Old owner only used vehicle for a few months of the year, so it is possible battery condition had dropped quite a bit. But I had taken it for a few trips into town and one big drive to give it a good run.

Garage thinks it could be a faulty thermostat. Temperature gauge takes quite a while for it to show and they had questioned that at the last service. I did notice radiator fan coming on when trying to jump start unsuccessfully and now know that standard jumper leads don't work for a diesel!

Thoughts on this? Just a flat battery?

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648 posts

Ultimate Geek

#3369464 1-May-2025 11:59

wouldn't be surprised if it's a battery issue. 3-year-old battery in a vehicle only used for a few months of the year.

borrow a charger that has a reconditioning mode (i use an MXS 5.0), to see if you can recover it (a bit).

hsvhel

1226 posts

Uber Geek

ID Verified

#3369467 1-May-2025 12:09

If it load tested fine...which was all they likely did, it would pass on a short burst

If it was depleted before you got it, possibility of one or more of the cells being sulfated and knackered.

Is the car charging it when running??

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tweake

2349 posts

Uber Geek

#3369469 1-May-2025 12:32

outdoorsnz:

dead flat (around 7.5 V

the battery is stuffed.

i've been through this recently. letting the battery go that flat usually kills it. they will often get an internal short. so it will discharge fine and pass a load test, but they will drain over time.

once you replace the battery, check its voltage during driving (i use a temp/volt gauge that plugs into the cig socket) to make sure its being charged ok.

nitro

648 posts

Ultimate Geek

#3369517 1-May-2025 12:38

tweake:

outdoorsnz:

dead flat (around 7.5 V

the battery is stuffed.

i've been through this recently. letting the battery go that flat usually kills it. they will often get an internal short. so it will discharge fine and pass a load test, but they will drain over time.

once you replace the battery, check its voltage during driving (i use a temp/volt gauge that plugs into the cig socket) to make sure its being charged ok.

i glossed over the 7.5V... at 10.5V it indicates a dead cell. time to recycle.

johno1234

2743 posts

Uber Geek

#3369529 1-May-2025 13:16

Going flat damages the battery. If storing a vehicle for a long time it’s a good idea to disconnect the battery or better still put it on a battery maintainer. Almost essential for boats and jet skis.

outdoorsnz

674 posts

Ultimate Geek

#3369554 1-May-2025 15:03

Thanks for all the reply's. Battery is now showing full green on the 2nd charger, so will turn it off and see if battery holds a charge overnight...

BUT. Not giving me much faith. Going to pop into town tomorrow and see an auto spark friend. New battery I'd say.

SATTV

1646 posts

Uber Geek

ID Verified

#3369555 1-May-2025 15:09

A friend of mine recently was telling me that there a quite a few lexus cars needing batteries replaced as they are not going far enough between starting and stopping to charge the battery, they apparently used a lot on the North shore to drop the kids to school and then go home or to the shops then home. The battery slowly looses charge and then wont hold enough charge to start a car.

Give the car a good run once you get the new battery, take the long way home.

John

I know enough to be dangerous

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johno1234

2743 posts

Uber Geek

#3369556 1-May-2025 15:11

outdoorsnz:

Thanks for all the reply's. Battery is now showing full green on the 2nd charger, so will turn it off and see if battery holds a charge overnight...

BUT. Not giving me much faith. Going to pop into town tomorrow and see an auto spark friend. New battery I'd say.

Heading towards winter which is not a great season for an iffy battery...

tweake

2349 posts

Uber Geek

#3369568 1-May-2025 15:37

SATTV:

A friend of mine recently was telling me that there a quite a few lexus cars needing batteries replaced as they are not going far enough between starting and stopping to charge the battery, they apparently used a lot on the North shore to drop the kids to school and then go home or to the shops then home. The battery slowly looses charge and then wont hold enough charge to start a car.

Give the car a good run once you get the new battery, take the long way home.

John

common problem with a lot of cars. my old work car has had that because work is not far away.

what makes it worse is replacing the old battery with calcium batteries. a lot of cars can't charge them fully as they need slightly higher voltage, so they are always undercharged to start with. also a lot of cars use EFB or AGM to allow faster charger due to the use of ecu controlled charging. ie they turn off the alternator to save fuel and turn it back on when going downhill (like ev regen). but if you put in a battery thats slower to charge up you can end up with a semi charged battery all the time. however EFB and AGM are expensive and tend to crap out quickly.

giving a car a good run doesn't do much except waste fuel. best thing is to simple put it on charge when you get home. the big factor in topping a battery up is TIME. you want hours not minutes. even weeks is preferred to hours.

i had an idea for an in car recharger for those cars who do short runs and can't connect a charger (eg parked on the street). nothing more than a trickle charger thats powered by a small battery, which in turn is charged from the car and/or solar. driving for a week chargers the small battery. when its charged and engine is off, it starts the trickle charger to top up the car battery. one day i might get around to making it.

outdoorsnz

674 posts

Ultimate Geek

#3369580 1-May-2025 15:55

tweake:

what makes it worse is replacing the old battery with calcium batteries. a lot of cars can't charge them fully as they need slightly higher voltage, so they are always undercharged to start with. also a lot of cars use EFB or AGM to allow faster charger due to the use of ecu controlled charging. ie they turn off the alternator to save fuel and turn it back on when going downhill (like ev regen). but if you put in a battery thats slower to charge up you can end up with a semi charged battery all the time. however EFB and AGM are expensive and tend to crap out quickly.

Forgot to mention that battery is calcium, hence the slow charge time. Car doesn't have start / stop technology.

Battery is now showing full green on two chargers, so will leave disconnected overnight and check in the morning.

outdoorsnz

674 posts

Ultimate Geek

#3369583 1-May-2025 15:58

johno1234:

Heading towards winter which is not a great season for an iffy battery...

As it stands, I'm not feeling very confident about driving to far. Not so easy to jump start a diesel.

Good thing I still have the good old reliable toyota corrolla with 380k's on the clock mostly all mine.

johno1234

2743 posts

Uber Geek

#3369584 1-May-2025 16:02

outdoorsnz:

johno1234:

Heading towards winter which is not a great season for an iffy battery...

As it stands, I'm not feeling very confident about driving to far. Not so easy to jump start a diesel.

Good thing I still have the good old reliable toyota corrolla with 380k's on the clock mostly all mine.

That 'rolla is only at half life as long as you change the oil...

johno1234

2743 posts

Uber Geek

#3369585 1-May-2025 16:04

If you can borrow a ctek battery charger from someone it will attempt to recondition the battery.

jnimmo

1097 posts

Uber Geek

#3369630 1-May-2025 20:30

Going through this at the moment too - battery is less than a year old. It's got at least a 3 year warranty on it, but of course that will depend on their test results and mean days without a battery while all that gets sorted out. I tried calling up Century directly as their website instructs you to do but they said I have to do it via the retailer (car dealer).

I just purchased a Victron Blue 4A charger, which gives you some nice monitoring via Bluetooth, in case anyone in Porirua needs to borrow one.. I've tried a recondition with that and if I have any more issues I'll give the warranty claim a shot.

Mine hasn't been hitting those low voltages though!

nitro

648 posts

Ultimate Geek

#3369632 1-May-2025 20:53

tweake:

giving a car a good run doesn't do much except waste fuel. best thing is to simple put it on charge when you get home. the big factor in topping a battery up is TIME. you want hours not minutes. even weeks is preferred to hours.

assuming you do a 30-minute drive, it will at least charge the battery enough for a couple of starts. obviously depends on other factors - state of the battery, parasitic drain, etc.

but i take it you mean it won't fully charge that battery, and you're right.

tweake:

i had an idea for an in car recharger for those cars who do short runs and can't connect a charger (eg parked on the street). nothing more than a trickle charger thats powered by a small battery, which in turn is charged from the car and/or solar. driving for a week chargers the small battery. when its charged and engine is off, it starts the trickle charger to top up the car battery. one day i might get around to making it.

"small battery" to charge a car battery? i'm skeptical. but i do hope you get around to making at least a prototype.

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