Battery Charger works but wont charge flat battery?
Discussion
TooMany2cvs said:
Problem is that a smart charger needs to "know" it's got the right type of battery attached before it'll start to charge, and it'll adjust the charging voltage/current to best charge the battery. If the battery's so flat that the charger doesn't "see" it, it won't charge it.
So you need a dumb charger that just blindly shoves out +14v whatever. Then make sure you don't leave it on for an extended period, because it WILL bugger the battery up...
It is 2 year s after the event but that is all you are doing when you fool the charger there is voltage in the battery. Turns the smart charger into something that kicks out a charge, leave it for a hour then disconnect, reconnect and bobs your uncle it reads the previous flat battery and charges it properly.So you need a dumb charger that just blindly shoves out +14v whatever. Then make sure you don't leave it on for an extended period, because it WILL bugger the battery up...
You might find just leaving it on for a few days might just work. My Saab had been sitting for a year with the battery connected. Obviously flat as flat can ever be. Jumped it, left it running for about an hour before getting it delivered home. So flat it wouldn't light the dash up. Ah well, no surprise there. On the bench connected to my charger it wouldn't kick in, it say there with the 'ready' light on; obviously no current being drawn. Normally I don't bother scratching around, but something made me leave it for, I think, 3 days. Stuck it back in the car just so I could move it, tried it for the hell of it and it started just fine. Been using the car about 1-2 times a week for just under a year now. It's made me respect Halfords batteries a lot more!
Annoying thing is, this Saab needs a thinner than normal battery otherwise it rubs on the turbo so I actually want it to die so I can get the correct size. I know it'll last for years now, until I drive across Europe minus jump leads or something.
Annoying thing is, this Saab needs a thinner than normal battery otherwise it rubs on the turbo so I actually want it to die so I can get the correct size. I know it'll last for years now, until I drive across Europe minus jump leads or something.
doogz said:
I think what it means is, connect your charger to your dead battery. Also connect a not-so-dead battery, to your dead battery, with a set of jump leads. The charger will recognise an amount of charge, and will start to charge your battery.
Not sure if you'll be able to disconnect the jump leads straight away, or if you'll need to leave it like that for a bit.
Just to say thanks for this tip. I forgot to connect the conditioner to my car after the last run - in September! Dead as a doornail yesterday, the trickle charger wouldn't register. I connected the lithium jump starter thing we keep in the other car and the conditioner, left it overnight and this morning it started. I will see how the battery is over the next few weeks but at least I could go for a drive in the sunshine this morning.Not sure if you'll be able to disconnect the jump leads straight away, or if you'll need to leave it like that for a bit.
I managed to reverse charge a flat bike battery last year. The bike had been in the shed for 2 years or so, the battery obviously utterly dead. I took it out, put it on charge and left it for a few days, all seemed good.
Plugged it back into the bike to get the engine turning only for nothing to happen. Found a blown fuse on the bike so I checked the battery and realised that when I'd been charging it I'd had the positive/negative leads opposite of how they were attaching to the bike.
Took it back out and put some glasses on (
) to realise I'd reverse charged it. Wasn't even aware such a thing could be done. 
I discharged the battery with a car headlamp over a few hours and then re-charged correctly this time. All seemed fine, but the battery couldn't hold a decent charge, probably due to the sulphated plates from being left discharged in the shed for so long, so I ended up buying a new one anyways.
Also, I had the Boxster stuck away for a few months last year, flat as a pancake, needed to open the hood to get to the battery to re-charge. The release on the hood is electric so I needed to get a 12v source onto the terminals inside the car. In the old days I could have used a battery charger for this, but modern chargers don't put out 12v unless they sense some kind of battery voltage. I ended up having to use a spare battery and some random wires with crocodile clips to apply the 12v needed to pop the bonnet.
Now I have the bike battery on the bench in the garage fully charged, and the boxster has a cheapie battery topper-upper from Halfords plugged in.
Plugged it back into the bike to get the engine turning only for nothing to happen. Found a blown fuse on the bike so I checked the battery and realised that when I'd been charging it I'd had the positive/negative leads opposite of how they were attaching to the bike.
Took it back out and put some glasses on (
) to realise I'd reverse charged it. Wasn't even aware such a thing could be done. I discharged the battery with a car headlamp over a few hours and then re-charged correctly this time. All seemed fine, but the battery couldn't hold a decent charge, probably due to the sulphated plates from being left discharged in the shed for so long, so I ended up buying a new one anyways.
Also, I had the Boxster stuck away for a few months last year, flat as a pancake, needed to open the hood to get to the battery to re-charge. The release on the hood is electric so I needed to get a 12v source onto the terminals inside the car. In the old days I could have used a battery charger for this, but modern chargers don't put out 12v unless they sense some kind of battery voltage. I ended up having to use a spare battery and some random wires with crocodile clips to apply the 12v needed to pop the bonnet.
Now I have the bike battery on the bench in the garage fully charged, and the boxster has a cheapie battery topper-upper from Halfords plugged in.
V8RX7 said:
Morningside said:
Due to some built in safeguarding system my 'intelligent' car charger will refuse to charge anything under 10 volts.
The cheap ones tend to do this - which makes them useless IMOThe CTEK regularly charges my 12v site radio from 7v
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