Crossed polls on car battery

ejcarey

Hi,

Yesterday evening whilst trying to start a oldish car off a spare battery I accidentally crossed the poles. Now I cannot even get the car to turn over, what would I have blown or what will I have to replace?

It is not as though I have never done this before, I have been jumping it for a week or 2 now. It has been off the road for 9 months and the battery was hosed before then but it always started off the spare until I crossed the poles.

You may ask why I did not just change the battery, but it is a A140 and anyone who knows them knows that the battery is in the drivers foot-well and it is a real nasty job to change it. I simply cannot remove the 2nd bolt.

Thanks
Eamonn...

cian1500ww

Is the ignition turning on or is it completely dead, no lights, gauges etc ???

DublinDilbert

Where/how did you short the battery?

Is there any chance a large fusable link near the battery has blown?

ejcarey

There is nothing, it is completely dead, not even a light on the dash. I crossed the poles when connecting the 2nd battery + --> - and - --> +.

Stupid I know, but it does happen.

cian1500ww

Check all your fuses, what type and year is the car ?

ejcarey

it is a 00 Mercedes A140 piece of S***

R.O.R

Do you have a voltmetre to check the batteries? I'd guess crossing the terminals has completly discharged both batteries.

ejcarey

I do indeed. I have pretty decent battery charger too so I will charge up the spare. The old one won't take a charge. I just want to get it to a garage to have some work done on it.

cian1500ww

ejcarey wrote: »

it is a 00 Mercedes A140 piece of S***

Worst case scenario would be that the onboard computer could be gone but that is worst case so it mightn't be that. I did it by accident when I jumped a an 87 fiesta from a 35 tractor, nothing was damaged not even the batteries :eek: Check all the fuses anyway and stick a good battery from another car into it. I'm imagine there should some sort of failsafe built into the car to prevent any damage being done but I'm not sure.

ejcarey

Knowing this car the worst case scenario is the most likely outcome. It was dusk when I was doing it so that is my excuse. I was starting it to drop it to the garage to have some work done on it today, ironically one of those things was to change the darn battery.

Esel

I don't know the battery compartment on the A series, but it is possible that you might be able to slacken the 2nd bolt if the other one is fully tightened. Generally, it is a good idea to slacken opposite bolts slightly in sequence, rather than loosen one fully first, as this can make the opposite one harder/impossible to turn.

macroman

Check the fuses. Likely hood is that you've blown a bank of them -- there should be some located under the bonnet and others on the main fuse board.

It might also be worth checking the batteries? It could just be a case that you discharged them.

colm_mcm

It's more than likely the main fuse, it should be between the + terminal on the battery and the main fuse box.

Midnight_EG

Alternator could be damn near fcuked, done it on a Focus before, it caught fire, might wanna check it

peasant

The possibilities are endless ...you could have fused several cells in one or two batteries (narrowly escaping an explosion ), blown a main fuse, burned wires to cinder or fried the complete electronics of the car.

Let someone in the know check it out

vw4life

colm_mcm wrote: »

It's more than likely the main fuse, it should be between the + terminal on the battery and the main fuse box.

thats most likely it alright,I think its built into the positive terminal connector at the battery

DublinDilbert

vw4life wrote: »

thats most likely it alright,I think its built into the positive terminal connector at the battery

+1

I said earlier in the thread it must be a fuseable link if your not getting anything at all... i should of been more specific...

cian1500ww

vw4life wrote: »

thats most likely it alright,I think its built into the positive terminal connector at the battery

Yeah, there should be some sort of failsafe in case of a mix up in polarity. It would be bad if Mercedes didn't incorporate something to protect the rest of the electronics.

Dartz

Think you might've damaged the battery, more than anything else.

Current would've taken the path of least resistance, so both batteries would've just discharged rapidly into each other. Wouldve dumped a lot Amps through the cables, but nothing at all should've flowed into the actual guts of the car.

Check your fuses.

Try charge the battery.

Try a brand new battery.

If none of these solve it, then call dead electronics.

vw4life

cian1500ww wrote: »

It would be bad if Mercedes didn't incorporate something to protect the rest of the electronics.

yeah,considering they made such a good job of the electronics in the first place