Can you charge a car battery off another car

Have a car thats in a position it can't be jumped and the battery is too flat that the battery charger won't work. Is it possible to take this battery out of the car and connect it via jump leads to a car that is running to give it a bit of charge? Tks

martyc5674

Yeah it will get some charge that way... however if your regular charger isn’t able to get life into it I doubt you’ll have any more success with the other cars alternator.

martyc5674

martyc5674 wrote: »

Yeah it will get some charge that way... however if your regular charger isn’t able to get life into it I doubt you’ll have any more success with the other cars alternator.

It's a mates battery its only 4 months old but the car hasn't been driven so I doubt it's gone. Hopefully doing this might then give it enough charge to let the charger do its work

martyc5674

Maybe you were trying to charge it with the terminals still connected?
If so 1. It’s not a good idea... could damage the car. 2. Smart chargers won’t always operate in this scenario as they can’t discipher what they are dealing with.

Gen.Zhukov

I did this a few years ago. Golf trolley 12v battery,flat as a pancake. Charger said no.
Hooked it up to the car and got a bit into it. Charger said yes.

Vronsky

Amaya Inexpensive Tether wrote: »

Have a car thats in a position it can't be jumped and the battery is too flat that the battery charger won't work. Is it possible to take this battery out of the car and connect it via jump leads to a car that is running to give it a bit of charge? Tks

Why not give it a push start?

punisher5112

Vronsky wrote: »

Why not give it a push start?

If it's dead and no lights on dash it won't push start.

Jump it from another car.

Connect red 1st then black and place black on dead car to chassis point.

Rev running car for up to 5 mins but keep eye on cables as can get extremely hot and make sure they are a decent type.

Rev it to around 2 to 2.5 rpm keep it steady.

Vronsky

Vronsky wrote: »

Why not give it a push start?

It's at the bottom of a driveway with an incline and has flat tyres

punisher5112

punisher5112 wrote: »

If it's dead and no lights on dash it won't push start.

Jump it from another car.

Connect red 1st then black and place black on dead car to chassis point.

Rev running car for up to 5 mins but keep eye on cables as can get extremely hot and make sure they are a decent type.

Rev it to around 2 to 2.5 rpm keep it steady.

I know how to jump a car lol it can't be jumped in the position its parked in

punisher5112

Amaya Inexpensive Tether wrote: »

I know how to jump a car lol it can't be jumped in the position its parked in

Pull it out. Or take battery out and do exactly what I said but obviously connect black to terminal.

JohnBoy26

Amaya Inexpensive Tether wrote: »

It's a mates battery its only 4 months old but the car hasn't been driven so I doubt it's gone. Hopefully doing this might then give it enough charge to let the charger do its work

It could be gone if it's been left to completely discharge

Irish Steve

The battery can be charged off the vehicle, but it will need a substantial charge before it will start an engine that's been lying idle for that length of time.

The other option is to find someone that has some real jump leads rather than the excuse for jump leads that are sold by too many places these days. I have a set that can reach the front of a long wheel base transit from a vehicle parked behind it, and they've been a lifesaver on more than a few occasions, such as on the hard shoulder of a motorway, you can't turn one of the vehicles round in order to get the batteries close enough to each other to start the dead one in that situation, which is the problem with too many jump lead sets these days.

A high capacity booster pack is another option, though even a good one may struggle if the battery in the target vehicle is completely dead, it will depend on the capacity of the booster pack and how new the pack is.

Irish Steve

Irish Steve wrote: »

The battery can be charged off the vehicle, but it will need a substantial charge before it will start an engine that's been lying idle for that length of time.

The other option is to find someone that has some real jump leads rather than the excuse for jump leads that are sold by too many places these days. I have a set that can reach the front of a long wheel base transit from a vehicle parked behind it, and they've been a lifesaver on more than a few occasions, such as on the hard shoulder of a motorway, you can't turn one of the vehicles round in order to get the batteries close enough to each other to start the dead one in that situation, which is the problem with too many jump lead sets these days.

A high capacity booster pack is another option, though even a good one may struggle if the battery in the target vehicle is completely dead, it will depend on the capacity of the booster pack and how new the pack is.

Thanks man, I think the course of action will be to just try to get enough charge into it that the battery charger will charge it rather than try to start the car directly off it .

Agree about jump leads, way too short.

rex-x

There is a really good chance if its that flat for that long then its dead, even if relatively new. They just cant cope with cold weather + low charge

Bazzy

I've done this before probably a bit on the bold side but it got me out of a hole

Good car running - take the battery out , replace with flat battery and see will that charge her up

johnayo

Bazzy wrote: »

I've done this before probably a bit on the bold side but it got me out of a hole

Good car running - take the battery out , replace with flat battery and see will that charge her up

Probably not the best advice. Plenty of potential to do damage to the slave car.

Irish Steve

Bazzy wrote: »

I've done this before probably a bit on the bold side but it got me out of a hole

Good car running - take the battery out , replace with flat battery and see will that charge her up

DON'T DO THIS, on a modern vehicle that has a lot of complex electronics, there is the potential to do massive damage to the electronics if there is no battery in the vehicle when it's running.

The only way to get round this if you want to fit the flat battery to the vehicle is to turn off, swap the batteries, then use jump leads to get it running again, leave the good battery connected for several minutes with the engine revs raised to charge the battery a bit, and then disconnect the good battery. Even then, check the voltage on the vehicle to make sure that it's not gone too high, if the bad battery is not taking a charge, there is the potential to do damage, and on modern vehicles, that can be seriously expensive to repair.

Del2005

Bazzy wrote: »

I've done this before probably a bit on the bold side but it got me out of a hole

Good car running - take the battery out , replace with flat battery and see will that charge her up

Would it not be easier just to remove the dead battery and connect it to the good car with jumper cables when it is running? Still not ideal though.

Cerco

So what will you do if you get the flat battery charged enough to start car, given you have two flat tyres?
Why not fix flats first and tow out so you can do a regular jump start?

Don’t fool around disconnecting batteries as you will cause issues in the donor car, as stated previously.

JohnBoy26

I never seen a flat battery cause the charger not to work. If its not charging the battery its either kaput or the battery is gone.

Irish Steve

JohnBoy26 wrote: »

I never seen a flat battery cause the charger not to work. If its not charging the battery its either kaput or the battery is gone.

Some of the newer chargers out there, (especially the smaller ones from Lidl and Aldi ) have inbuilt controllers that won't let them start charging if they don't see valid voltages from the connected battery. The only way round it is to parallel connect a good battery to get the charge started, and then see how it works out after that, which can be tedious.

JohnBoy26

Irish Steve wrote: »

Some of the newer chargers out there, (especially the smaller ones from Lidl and Aldi ) have inbuilt controllers that won't let them start charging if they don't see valid voltages from the connected battery. The only way round it is to parallel connect a good battery to get the charge started, and then see how it works out after that, which can be tedious.

It seems pretty pointless having a charger that won't charge a flat battery.

rock22

JohnBoy26 wrote: »

It seems pretty pointless having a charger that won't charge a flat battery.

What Irish Steve said applies to almost all modern chargers.

Del2005

JohnBoy26 wrote: »

It seems pretty pointless having a charger that won't charge a flat battery.

To get a completely dead battery back to life requires a lot of energy, the cheaper battery chargers aren't built to supply the required energy so default to not charging if they don't see a voltage. Spend big money on a charger and they will recover a dead battery, but unless you regularly let multiple batteries completely die it's cheaper to buy a new battery and a trickle charger.

Isambard

apparently push starts are not recommended in many instances. Damages the cat I'm told. Tail caught in the fan belt maybe?

Isambard

Put good battery in car with flat battery, start car, reverse out to position where a jump start could (carefully) take place, switch batteries back....you see where this is going?

Del2005

Isambard wrote: »

Put good battery in car with flat battery, start car, reverse out to position where a jump start could (carefully) take place, switch batteries back....you see where this is going?

For some unknown reason they won't pump the tyres in the dead car so it can't be moved.

punisher5112

I can't believe it's gone 3 pages.....

shietpilot

Just remove the good battery, bring it to the car with the flat battery and jump it from the battery. Simples. No need for a full car