What's a reasonable number of times to be asked to give a jump start?

[Alan]

In message , Gib Bogle wrote

Try and start a car on a dying battery and it will be the same as removing it.

[Tim Watts]

Makes you wonder if the morons have discovered the joys of E2 or flash non volatile memory...

The bit about BMW being "clever" re having a new battery for the benefit of the charging circuit is the only valid one I can see - but BMW have been trying to stiff non BMW servicing since at least the later 80's.

[Dave Plowman (News)]

Maybe not. Once the battery gets below a certain level the starter (and the relays) which operate it won't work. But there may still be enough volts to keep memories alive.

[Matty F]

I have successfully swapped the battery without losing the voltage to the car. Because the old and new batteries were extremely large and heavy, I had to get into the boot to lift them. There was not enough room for me plus two large batteries in the boot. I wired up a third small car battery and the swap was easily done. I need not have bothered, since months later the car appeared to be on fire, so I disconnected the battery in case it was a wiring short. I had to key in the radio code but everything else worked OK. I was surprised to find that the radio remembered all of its settings even though the power was off for a couple of weeks.

[Ian Jackson]

1. Slacken the bolts on the battery connectors.
2. Make sure that the connectors are loose, but don't disconnect from the battery terminals.
3. Connect the jumper lead clips to the connectors.
4. Ease the connectors off the battery terminals.
5. Replace battery.

1. Put the connectors on the battery, making sure that they are a push fit (tighten/slacken bolts as necessary).

2. Remove jumper leads.

1. Tighten connector bolts.

That ought to work. The car electrics will never know you did it.

[Tim Streater]

Exactly. Perhaps some car expert could explain why it should make a scrap of 'king difference that the power is removed from the electronics from time to time. No other piece of kit is affected this way.

[Tim Streater]

You don't need volts to keep memories alive, and haven't ever since eeprom was invented - in 1978.

[Ian Jackson]

In message , Tim Streater writes

Yebbut..... Having a volatile memory is a nice little earner, innit? Stop rocking the boat!

[Tim Watts]

I want to drill holes in the boat, kick it over, dowse it in petrol fire flares at it from my boat then play Harpoon Willy with the survivors!

[Scott M]

I had my first BMW about 8 years ago and I was surprised at how forward thinking they were and how well engineered stuff was (having believed all the negative hype about them before.) Things like threaded holes on the water pump so you could just pop a couple of M8 bolts in and use them to wind the pump out of the block. Beat the application of the /large/ hammer that Vauxhalls required, for instance.

Now though they do seem to have started putting stuff in just to the disadvantage of the owner.

Peversely, on my L-reg 3er they had a magnet & hall-effect switch that counted pulses of the winder motor and would shut it off if the pulses stopped coming. On my '54 plate 3er the strip at the top of the window simply activates a microswitch. So that's gone backwards.

Mind you, the 5er upwards always seems to be a testbed for Bizarre Things. The anti-trap mechanism on those probably consists of a bottled Genie that watches from the B-pillar.

[Dave Liquorice]

And me, used a small 12v SLA battery, plugged into lighter socket via a fused lead. You probably have to put the ignition switch into the "aux" position to get power to the lighter socket and thus a circuit to power the car when the main battery is disconnected. Don't turn to "run" or "start"... (that's why I used a fused lead).

[Frank Erskine]

No - it's the wrong time of year for Lent :-)

[Dave]

I can't understand why anyone would want to buy one. The slightest hint of ice or snow and they are stuck at the side of the road.

Dave

[Dave Plowman (News)]

My brother seems to manage ok with his 330T. In the NE of Scotland. Ordinary tyres with rear ones dropped to 20 psi. Couple of bags of salt/grit in the back and some old mats in case things get really bad. SIL manages it too. And they're both OAPs.

When people get stuck at the side of the road it's usually down to them - not the car.

[Gib Bogle]

This is the tricky step. At this point there is a jumper lead clip on the battery terminal, and the other clip is on the battery connector. You have to get the connector onto the battery terminal which has a jumper clip on it. The clips are usually quite large, comparable in size with the terminal. Care will be needed to make sure that the contact between the connector and the terminal is maintained while the clip is removed from the terminal.

[Ian Jackson]

Before starting the job, you obviously need to assess the possible snags that might arise, and prepare for them. The cigar lighter connection is obviously easier, provided it works (which it ought to).

[Harry Bloomfield]

Tim Watts submitted this idea :

Mine uses the current draw of the motors, to work out where its fully open/closed positions are - simples.

[Harry Bloomfield]

Tim Streater was thinking very hard :

Whilst that is true, it relies on the manufacturers to fit EEPROM. Then if it is used, then quick way of resetting the ECU to get it to relearn its settings (battery disconnect), would be lost.

[ARWadsworth]

Not on these jump leads. They are 25mm CSA with proper hydraulic crimped clips. They were custom made some 20 years ago so that they would be long enough to jump start a a Ford Sierra with a MKII Escort with one in front of the other and not side by side or facing each other.

[Harry Bloomfield]

Ian Jackson expressed precisely :

Only if the lighter socket is permanently live!

A better method than connecting across the battery leads, is to find the under-bonnet main fuse box and seeing if there is an accessible live all the time bus bar. Connect to that and a good ground/ earthed engine part.