Bump start a car with no battery?

[braddo]

If the battery has been removed from a car is it correct that it can’t be bump started?

I am guessing the loose battery leads mean a break in the electrical circuit if nothing else?

Maybe an old car with points ignition could still be started but for a car with an immobiliser and electronic fuel/ignition, no battery means no go?

Basically, the reason for asking is whether a car is any more or less secure with its battery removed (needs a recharge...) compared to a charged battery and immobiliser active.

[braddo]

The main reason for asking is that I had to take a battery out of a car to recharge it, and does doing so make the car any less resistant to theft?

Removing the battery means the engine immobiliser is no longer active. But then if it's impossible to get the car going without fitting a battery, then the theft risk hasn't risen.

The odds of theft are low (touch wood), but I don't want to inadvertently make the car easier to steal and risking insurance cover.

[braddo]

rockin said:

For those who are interested,
Old cars had a "dynamo" to charge the battery. A dynamo has physical magnets in it and can only generate a small amount of DC electricity. Any time the shaft is turned the rotating coil produces electricity as it moves through the magnetic field. Hence a car which is pushed along the road in gear will have electricity to fire the coil and plugs as soon as the clutch is released.
Modern cars have an "alternator" to charge the battery. An alternator has no magnets, just two different sets of coils which interact with each other and generate a huge amount of AC electricity. (Hence the need for diodes/rectifier to convert it to DC for your car.) One set of coils must be "energised" with electricity from the battery to produce a magnetic field and the other set of coils then rotate through that field to generate electricity. Hence if there's no battery installed or if it's completely flat your alternator won't work at all and your car can't be started by being pushed.

[braddo]

stevieturbo said:

braddo said:

Basically, the reason for asking is whether a car is any more or less secure with its battery removed (needs a recharge...) compared to a charged battery and immobiliser active.

You can tow it away regardless, fire it onto a trailer etc etc.

Is it at any particular risk of theft ?

Indeed, I would agree the bigger risk is that the car is lifted away. I don't think there's any particular risk of theft (touch wood); it was more a question of is the car any less secure by having no battery.

One could imagine an insurance company taking the angle that because the anti-theft protection (immobiliser) was not 'active', it was therefore easier to steal.

Not sure there any many car thieves out there who can be arsed trying to drive off in a Caterham with no steering wheel, no battery and a recalcitrant immobiliser. It would be enough of a hassle just getting into the driver's seat with the hood on.

[braddo]

Good point. I don’t know. By inactive, well, I mean the red light doesn’t flash any more! But it makes sense that if I immobilised it before the battery went dead, it won’t just mobilise itself by reconnecting the battery.

[braddo]

Chris32345 said:

At imboliser is always active
It needs to be energised to turn it off

Or else they would be too say to bypass

My Caterham is 90s vintage so the immobiliser needs to be activated mnaually (button on key fob). I suppose as long as it is activated before the battery goes dead, the immobiliser is active when the battery is reconnected. Therefore it's no easier to steal with a missing battery, which was my original question.

When I put the battery back in last weekend it did take a few attempts to turn off the immobiliser and get it started.