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Car Battery Flat Won't Charge


gibbon

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Brought a new battery about 10 months ago. It's gone flat twice. First time I just assumed I left the lights on or something. Second time a few days ago after leaving the car without driving it for 2 weeks, even with a solar trickle charger plugged in, realised I must have a parasitic draw on the battery.

Now my issue before I find the parasitic draw is I can't charge the battery. I've got a digital smart 6v/12v battery charger. The battery's initial charge was 4v. The charger won't charge it above 5.4v. I believe it thinks it's a 6v battery. There's no option to switch modes. 

So what are my options to get this sorted? Is the battery recoverable? Someone suggested buying an old "dumb" battery charger? Should I take the battery back (it's still under warranty) or are they just going to tell me to do one?

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7 minutes ago, Kurt Barlow said:

Try desuplhating it.

You will probably need to do it for several days. 12 hour desulphator followed by 12 hour charge. 

That won't change the voltage though will it? Because it's gone under 6v my charger thinks it's a 6v battery

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belfastchild

Older chargers will work, the non smart type, just leave it on for a while. My smart charger wont charge anything under 11v or something around that.

If its 10 months old, take it back and ask them to sort it.

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Aren't car batteries the old type that if left to drain too far are unrecoverable? If , see if can replace the liquid in it, even 'sealed for life' aren't really as far as I know. Though if it's that new surely some sort of guarantee is still in place.

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Kurt Barlow
2 hours ago, gibbon said:

That won't change the voltage though will it? Because it's gone under 6v my charger thinks it's a 6v battery

sounds like you need a dumb charger. 

If its run down like that over a long period and in low temps the battery will be fubarred. 

 

Edited by Kurt Barlow
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Andersen

As said above, try a vintage dumb charger, they pump 12v into the battery regardless of the condition.

I have an Optimate smart charger and rate it highly but it won't attempt to charge unless it's connected to something it recognises as a part charged 12v battery. I use an old transformer style charger to get some life into a dead battery, then leave the smart charger connected for a couple of days. Old lead batteries often kill one or more cells (2.4 volt each?) so the battery will can never be fully recovered. 

I left a sealed gel battery on a parked modern car for several months and it went down to 2 volts, I was very surprised that it recovered to 100% :Beer:

Edited by Andersen
For your parasitic draw, check courtesy light in the boot and any aftermarket radio (if you can turn the radio on without inserting the key - the radio is the culprit)
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Got another car or access to one?  Use the battery from that to give it an initial charge.  Might be lucky and be able to revive the flat one with a full charge but often if left at a low voltage for period of time they've degraded too much.

It's a faff turning it on and off but if you have a parasitic draw and can't find it an earth disconnect under the bonnet or on the battery terminal is useful if you know the car is going to be left a while.

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Mirror Mirror

I d read that a fully discharged lead acid battery is scrap, with fully discharged meaning <11 volts.

If it’s got a guarantee, take it back, they aren’t going to quibble.

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Cheers all, had a look on FB marketplace for a dumb charger thinking I could pick something up quickly local for a tenner. Nope, just a few dreamers wanting £40 for their POS "vintage" battery charger from the 1970s FFS. 

Decided to get a mate to jump start me, thinking if I could get the battery above 6v charge my charger would then recognise it as 12v. Drove it for an hour, engine off, used multi-meter and it's measuring 12.6v. Engine starts fine. Took @onlymeadvice and will keep the battery disconnected until I find the parasitic draw. 

Regarding battery health, does the fact it recharged to 12.6v indicate it's still good health? I know with the li-ion batteries on my e-bike the max voltage decreases as the battery health/capacity drops but not sure if it's the same with car batteries?

15 hours ago, MrPin said:

This could be a world changing problem.

Fuck. Off. 

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1 hour ago, gibbon said:

Cheers all, had a look on FB marketplace for a dumb charger thinking I could pick something up quickly local for a tenner. Nope, just a few dreamers wanting £40 for their POS "vintage" battery charger from the 1970s FFS. 

Decided to get a mate to jump start me, thinking if I could get the battery above 6v charge my charger would then recognise it as 12v. Drove it for an hour, engine off, used multi-meter and it's measuring 12.6v. Engine starts fine. Took @onlymeadvice and will keep the battery disconnected until I find the parasitic draw. 

Regarding battery health, does the fact it recharged to 12.6v indicate it's still good health? I know with the li-ion batteries on my e-bike the max voltage decreases as the battery health/capacity drops but not sure if it's the same with car batteries?

Fuck. Off. 

There will be some degradation, possibly a lot, might work OK for the summer then when it gets cold you'll know. Health and capacity and more importantly for starting cranking amps drop, all battery chemistry does.

Highly recommend one of these, will tell you battery health very predictably, take it round to nearest scrappy or reclamation centre and you can pick out the best replacement battery for pennies on the pound.

https://www.ebay.co.uk/itm/354134631730

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12 minutes ago, onlyme said:

There will be some degradation, possibly a lot, might work OK for the summer then when it gets cold you'll know. Health and capacity and more importantly for starting cranking amps drop, all battery chemistry does.

Highly recommend one of these, will tell you battery health very predictably, take it round to nearest scrappy or reclamation centre and you can pick out the best replacement battery for pennies on the pound.

https://www.ebay.co.uk/itm/354134631730

Thanks i'll look into getting one of those, great tip on using it at the scrappy. The battery is still under warranty so if it dies again in winter I'll be getting it replaced.

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belfastchild
37 minutes ago, gibbon said:

Thanks i'll look into getting one of those, great tip on using it at the scrappy. The battery is still under warranty so if it dies again in winter I'll be getting it replaced.

If you bring it back to where you got it they will probably have one of those and test it for you.

Charging to a voltage is no sign of health, connect a load and it might drop straight down to 6v or whatever.

I wouldnt wait until it was out of warranty to get them to check it. Like all batteries and backups the first time you find out they have failed is when you really need them. There will be a lot of people looking replacement batteries in the winter, I try to test all mine and sort out the dodgy ones towards the end of the summer.

If its tested ok, just run your newer trickle/smart charger on it for while. Pita I know but might clear the plates.

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nirvana
4 hours ago, gibbon said:

Regarding battery health, does the fact it recharged to 12.6v indicate it's still good health? I know with the li-ion batteries on my e-bike the max voltage decreases as the battery health/capacity drops but not sure if it's the same with car batteries?

i've had issues with car batteries the last few years, mainly cos I never use the fukkers lol

Anyways I can start my Civic with a battery that shows only 11.65v so anyone who says a battery is fukked showing less than 12v is talking shite :P

I also have a stupid Mini with a BM battery and I thought that was totally fukked at less than 10v but I borrowed a vintage German charger from a mate and it's been fine after an overnight charge, that was over 6 months ago now....

anyways thanks for the heads up I'll go and check my currents voltages u idiot xD

Edited by nirvana
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nirvana

12.45v (happy with that) and 11.86v - not good will get the charger out......

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Is the car old ? I had this issue with my old Bora. Some form of parasitic draw. A cunt to try and work out. 

Switch everything off then find the fusebox then use the multimeter as a fuse type thing itself. All should be zero. 

Unfortunately for me the few that weren't - when I got the fusebox chart online - were things you might expect to still be on even when car off. Computer type stuff etc.

So I still couldn't work out. 

 

 

 

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42 minutes ago, ccc said:

Is the car old ? I had this issue with my old Bora. Some form of parasitic draw. A cunt to try and work out. 

Switch everything off then find the fusebox then use the multimeter as a fuse type thing itself. All should be zero. 

Unfortunately for me the few that weren't - when I got the fusebox chart online - were things you might expect to still be on even when car off. Computer type stuff etc.

So I still couldn't work out. 

 

 

 

It's all the alarms, immobilisers, and such that cause unwanted battery drain. I had one car that wouldn't last 3 weeks of idleness. Current one can do a few months.

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belfastchild
43 minutes ago, MrPin said:

It's all the alarms, immobilisers, and such that cause unwanted battery drain. I had one car that wouldn't last 3 weeks of idleness. Current one can do a few months.

I had one where the pioneer head unit (organic display or whatever the fuck that was all about) was a massive drain. Swapped it back for the oem blaupunkt and no more problems.

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1 hour ago, belfastchild said:

I had one where the pioneer head unit (organic display or whatever the fuck that was all about) was a massive drain. Swapped it back for the oem blaupunkt and no more problems.

I think this is quite a common issue, change to ignition switched supply and settings lost on some so often wired in permanently. A lot of bad design out there.

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Andersen
2 hours ago, belfastchild said:

I had one where the pioneer head unit (organic display or whatever the fuck that was all about) was a massive drain. Swapped it back for the oem blaupunkt and no more problems.

Not a problem with the hifi (I have the same one), it’s dodgy wiring.

radios have 2 wires, one tiny one to remember radio stations etc, one big one for display and sounds - this should only get power when the key is on, if it’s wired wrong it will give you a flat battery in a few days. Last ca I bought had this problem so it’s fairly common :S

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belfastchild
3 hours ago, onlyme said:

I think this is quite a common issue, change to ignition switched supply and settings lost on some so often wired in permanently. A lot of bad design out there.

 

2 hours ago, Andersen said:

Not a problem with the hifi (I have the same one), it’s dodgy wiring.

radios have 2 wires, one tiny one to remember radio stations etc, one big one for display and sounds - this should only get power when the key is on, if it’s wired wrong it will give you a flat battery in a few days. Last ca I bought had this problem so it’s fairly common :S

This one had both ACC and +12v wiring. Was definitely something internal. Replaced like for like with the blaupunkt and no problem (it had the display as well).

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Andersen

@belfastchild understood but I know pioneer kit well, they often have a wiring harness so you can easily swap the 2 wires.

If the wires are connected “backwards” the radio appears to work but soon drains the battery. Or maybe yours was faulty - could be either. Glad you got it sorted :Beer:

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Roger_Mellie
On 25/07/2022 at 09:17, gibbon said:

That won't change the voltage though will it? Because it's gone under 6v my charger thinks it's a 6v battery

I had this problem, I just left it for a few days and it worked itself out. 

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