Changing car battery

[Stewart7]

Dear All

Before changing my car's 12volt battery, would it be a good idea to wire some 'D' cells together to make 12 volts, and connect them to the car battery leads using crocodile clips, so as to keep everything powered while the main battery is changed?

I wondered if this could be a way of avoiding any sort of shock to the car's electronics, and also to avoid having to reset things like electric windows.

Or am I worrying too much again!

[J.R.]

No, then Yes.

[SuperbTWM]

Sorry, read 'charged' not changed.

 

I should sleep now

Edited 6 April, 2020 by SuperbTWM

[Stewart7]

Sorry folks, Thank you for taking the trouble to respond, but this 72 year old brain is just confused by your answers.

 

I know from bitter experience that any electronic equipment does not like its power supply disconnected or connected, but prefers a constant steady supply.

During previous car battery changes, I've always cringed if I wasn't able to attach the last cable quickly and make a nice clean connection, and thats before the days when cars were packed with electronics.

[Breezy_Pete]

Just disconnect the old one, negative lead off first, then positive. Remove old battery.

 

Place new battery in position and clamp down.

Reconnect positive lead; reconnect negative lead. Don't be alarmed at all by the spark that happens when you do this last thing, it's quite normal and not dangerous to you or the car.

[flybynite]

Personally I set my battery charger to 'supply' and connect it whenever I take a battery out because I cannot be bothered to enter codes and clear fault codes on cars that need it.

 

Not going to be the end of the world if you don't.

 

If you are gong to be changing the battery, you do know the new battery needs to be coded to the car? I.E the car needs telling it has a new battery and what type.

 

If you are just charging it then connect the charger to the battery before connecting the charger to the power and make sure you have the correct charger for the battery type (AGM etc.)

[xman]

23 hours ago, Stewart7 said:

Dear All

Before changing my car's 12volt battery, would it be a good idea to wire some 'D' cells together to make 12 volts, and connect them to the car battery leads using crocodile clips, so as to keep everything powered while the main battery is changed?

 

No it sounds a very dangerous thing to do.

Not only might your car battery attempt to dump a load of current into the D cells with catastrophic results, its doubtful if the D cells would be able to maintain a stable voltage should you accidentally open a door and wake the cars electronics, pumps etc up.

 

Unless you have a professional bit of kit designed to maintain the voltage, just follow the instructions in the manual, which from memory is to remove the negative lead first. 

 

When reconnecting, negative lead is last to go on.

 

Make sure the car is unlocked while your doing it and you have the keys OUTSIDE the car, well clear of it, if its KESSY

 

Car should be fine, you might have to reset the clock.

 

Remember if fitting a new battery, it will have to be coded in using a tool like VCDS or OBDELEVEN otherwise you could have problems further down the line.

[Stewart7]

28 minutes ago, xman said:

 

No it sounds a very dangerous thing to do.

Not only might your car battery attempt to dump a load of current into the D cells with catastrophic results, its doubtful if the D cells would be able to maintain a stable voltage should you accidentally open a door and wake the cars electronics, pumps etc up.

 

Unless you have a professional bit of kit designed to maintain the voltage, just follow the instructions in the manual, which from memory is to remove the negative lead first. 

 

When reconnecting, negative lead is last to go on.

 

Make sure the car is unlocked while your doing it and you have the keys OUTSIDE the car, well clear of it, if its KESSY

 

Car should be fine, you might have to reset the clock.

 

Remember if fitting a new battery, it will have to be coded in using a tool like VCDS or OBDELEVEN otherwise you could have problems further down the line.

Thanks for the warning.

[Stewart7]

So.  I must read the handbook, and maybe let Halfords change it.

 

Thanks to everyone.

Stewart

[J.R.]

If your car does not have a stop start system then you are free to change the battery yourself, the radio will not need recoding, any warning lights for ABS, steering etc will go out within a few yards of driving, the fault codes will be deleted after a certain number of no fault engine starts, you do not need to maintain voltage while changing the battery.

 

Regarding all the well meaning advice regarding the handbooks saying remove negative terminal first, before passing it on do any of you know or understand the reasoning behind it? Oncee ither terminal is disconnected neither the battery nor the vehicle will know nor care which one it was.

 

In the days of metal bumpers and vehicles having either +ve or -ve polarity there was a logical safety protocole when jump starting a vehicle from another regarding connection and deconnection.

 

Personally I always disconnect the +ve cable first but more importantly remove both terminals to isolate the vehicle electrics, removing just the negative lead I suppose could avoid the situation of a spanner or other metallic object shorting the positive terminal or starter cable to the chassis.

Edited 7 April, 2020 by J.R.

[langers2k]

1 minute ago, J.R. said:

Regarding all the well meaning advice regarding the handbooks saying remove negative terminal first, before passing it on do any of you know or understand the reasoning behind it? Oncee ither terminal is disconnected neither the battery nor the vehicle will know which one it was.

 

 

Yes - it's to reduce the risk of a short circuit whilst undoing the clamp.

 

If you undo the negative clamp first, the clamp, your metal tool and the cars bodywork, engine and other earthed metal components will be at the same potential so the risk of short circuit is low.

 

If you undo the positive clamp first, the clamp, your metal tool will be at ~12v so touching the cars bodywork, engine and other earthed metal components will create a dead short across the battery.

 

Obvious the opposite is true for older positive earthed vehicles.

[J.R.]

Thanks for that, I will have to make a positive effort (see what I did there!) to change the habit of a lifetime.

 

Mind you, you would have to be really lucky to find any metal amongst all the plastic in a modern engine bay!

[PetrolDave]

11 hours ago, langers2k said:

If you undo the positive clamp first, the clamp, your metal tool will be at ~12v so touching the cars bodywork, engine and other earthed metal components will create a dead short across the battery.

It's surprising how much of a spanner a battery can melt .....

[flybynite]

12 hours ago, PetrolDave said:

It's surprising how much of a spanner a battery can melt .....

 

Indeed!

 

I split the battery on the occasion I did it in the past and couldn't un-weld the spanner quick enough. 💥