Nightmare Jump Start - Peace of Mind Needed

Andrew Brockbank · May 5, 2019

static zap said:
The cheaper your leads ,the better chance of no damage !
( ECU's spike even with the correct polarity )
Is his alternator still charging ? (is a good question)...
May have shunted -power !
..If drains quickly over night
a) Battery now shot
b) Something is damaged and taking power when off.. Alternator classic

The alternator of mine (good battery) or the other car (bad battery) is likely to be the one that's damaged?

Andrew Brockbank · May 5, 2019

static zap said:
The cheaper your leads ,the better chance of no damage !
( ECU's spike even with the correct polarity )
Is his alternator still charging ? (is a good question)...
May have shunted -power !
..If drains quickly over night
a) Battery now shot
b) Something is damaged and taking power when off.. Alternator classic

The alternator of mine (good battery) or the other car (bad battery) is likely to be the one that's damaged?

ruston · May 5, 2019

Andrew Brockbank said:
The other car didn't start after that unfortunately. It's likely it's killed it. It's a £300 beater on its last legs, we are more worried about the damage that may have been done to my car.
The other car is pre 2000, so we are replacing the battery and ECU, if this doesn't work it'll be a scrap job.

If after 100 miles you have had no problems and your alternator is not showing the warning lamp there is a good chance you have got away with it. It seems his car has taken the brunt of the reverse polarity.

static zap · May 5, 2019

If your battery was strong ,and his weak ,your battery probably will survive. His alternator is at risk , since his battery was most likely to reverse polarity !
As for your car charging -fans should speed up a little
and lights run brighter with engine running (..or a cheap
voltmeter ! rising to 14.0 14.4 ish ) and no warning light !
--

Andrew Brockbank · May 5, 2019

Really appreciate all of the help.
As soon as the bank holiday is over I'll be straight into an auto electricians. I'll keep you posted on the outcome of both cars.

telectrix · May 6, 2019

start with just the battery, better still you can usually get a reasonable one from local auto breakers for a tenner or so. then if it works, consider a new battery.

Andrew Brockbank · May 6, 2019

telectrix said:
start with just the battery, better still you can usually get a reasonable one from local auto breakers for a tenner or so. then if it works, consider a new battery.

Cheers will do. An ECU for her polo is only £20 on eBay, sounds like there isn't a lot to them and it's plug and play (she's got an X reg 6n2, no immobilizer or central locking). I think both for the peace of mind, but the car isn't worth as much as an alternator would be.

Are you recommending I also get a new battery on my car?