Changing a car battery

[Matty F]

I've unsuccessfully tried to change a car battery before, without losing all the settings for the radio, trip computer etc etc. And without having to go and find the radio security code. It's easy enough to connect the new battery in parallel with the old using a couple of wires. But when I go to put the connectors on the new battery there's no way to do that without getting the wires out of the way.

What works as I discovered, is to have a third battery and connect the temporary wires to that. Just be sure to have a cord to tie the positive connector up out of the way while removing the old battery.

If I could trust the cigarette lighter socket I could connect a battery to that. But often the socket is disconnected when the ignition is off.

[Dave Plowman (News)]

I have a jump start pack which makes this quite easy - although you might have to tape its crock clips in place to avoid them popping off when you move the battery leads. But of course you have to be careful to avoid shorts too.

[Dave Plowman (News)]

Then the manual is written by an idiot.

Any backup storage system will have a finite life too.

[gb]

Wouldn't it just be easier to keep the security code card in your wallet/purse?

[Matty F]

The code is with my manual. I've never had to use it. I really don't want to have to reprogram all the radio stations.

[Tinkerer]

Since the start of this century most Peugeots, and I assume other makes, have had no need of codes because the radio is paired to the onboard computer. You still lose your tuning settings though. The handbook ought to tell you if yours requires a code.

Second point - I saw, a while back, a cable for sale with a cigarette lighter style plug at each end for exactly this purpose. You abviously need to ensure that your lighter does not power down with the ignition though. And don't try it with an older car with positive earth connections.

[Matty F]

Jaguar Cars Ltd.: "Under no circumstances should a battery be disconnected whilst the ignition circuit is live, as permanent damage to the instrument cluster may occur." I think they have a good point.

[tony sayer]

In article , Matty F scribeth thus

Arse protecting on a grand scale or very poor design?..

Which?..

[ARWadsworth]

But you are not disconnecting a battery whilst the ignition circuit is live. The power is supplied via the cig lighter and the instrument cluster would not know any difference.

Adam

[Bob Eager]

And the manual is kept in the car?

[Fredxx]

Some jump start packs might have a higher terminal voltage than from a 12v car battery. I'd measure it first.

[Dave Plowman (News)]

All the ones I've seen have a 12 volt SLA battery. But car electrics actually run on up to about 14.4 volts - not 12. And should be safe to rather higher than this to prevent an alternator fault frying them.

[Dave Plowman (News)]

They likely mean while the engine is running. A very different kettle of fish.

Anyone who designs electronics which can be damaged by the removal of power - and nothing else - should change to knitting. Because sooner or later this will happen - regardless of backup batteries.

[Steve Walker]

Aparently the "smart" charging system on Fords can put out up to 18V if your battery is flat, everything is cold, etc. hence them requiring "hi-tec" batteries.

SteveW

[Andy Champ]

what make of car?

My Toyota and my wife's Suzuki didn't turn a hair when I disconnected the old battery and put a new one in. No funny codes, no retuning, just reconnect and go.

Andy

[Matty F]

There are actually four manuals. The security system manual is never in the car.

[Matty F]

I've never had a problem changing car batteries or using jumper leads. But I've heard stories about computers being fried. My jumper leads have a device on them to "help stop damage". I don't know if this is a complete fraud or a protection against people who do something wrong. But what could be done wrong? Perhaps a voltage spike, and the old flat battery may not stop that.

In my case I could have made a mistake with an accidental short. I had basically three 100AH batteries in the boot, and I was in there too as the batteries are very heavy. The potential for flying molten lead was real. I did wear safety glasses.

[Matty F]

It's a Jaguar. But my Mazda loses everything when I disconnect the battery, and ditto for all other cars I've owned. I'm not happy using the cigarette lighter socket for anything important. I've had the plug move or come unplugged at the wrong moment. My jumper leads with alligator clips don't come undone!

[David J]

Halfords sell a little gadget just for this very purpose.

"Computer Memory Saver" from Draper, Type CMS1. It plugs into the cigarette lighter socket. I have one myself, and it works fine.

David

[geoff]

In message , David J writes

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