Car Battery

[Andehh]

Long story short I just got back from a week long holiday. Whilst on holiday I left a carPC plugged in. Being a computer it is a constant trickle drain on the battery. Usually this isn't an issue as I do a lot of long journeys & disconnect it when the car is left standing. This time I forgot though and the car won't start.


I have tried jump starting it off a neighbours car (watching her shunt her car closer & closer to mine was the most painful experience ever) and tried an ebay special battery starter both of which failed to produce any results.

I am hoping it's just a knackered battery, but is it worth calling the RAC out just in case? Do they have any ways of deep charging(?) or boosting a near empty battery? The locks still work, lights go off as per normal on dash so there is still something left in it but with the jump start & battery booster not working I am somewhat in the middle!

cheers guys

[Eagerbeaver]

Is the jump start not even turning the engine over? If not then you have either a bad connection with the jump leads or rubbish jump leads.

I've never used the cigar lighter ones so I don't know what they are like. If you can't get a jump then I suggest getting the RAC out as their leads are huge!!

If the battery is knackered after such a short spell of discharge - it was probably on its way out anyway.

Edited by Eagerbeaver on Wednesday 29th December 10:51

[oldcynic]

Get the RAC to jump start it (assuming you've got homestart). That's what you pay your subscription for! Don't buy a battery from the RAC.

Take it for a good long drive (20-30 minutes I would guess). If you get a flat battery again in the next few days then you need a new battery, and can shop around appropriately. If it carries on working then don't bother.

If the car hasn't been used in over a week it will take a bit more cranking than normal to start, hence the difficulty jump starting.

[Andehh]

Nope, the engine wouldn't even crank. Lights would flicker & die on dash and starter motor wouldn't catch on.

The car we were junping off a Saxo so hardly pumping with energy, same with the Ebay battery booster.

The fact the locks work & dash lights up as well as carPC turning on makes me think the battery wasn't utterly discharged so might be lucky. Any other comments would be appreciated!

[varsas]

How long did you leave the cars connected for? Usually when you jump start a car you don't try and start the dead car off the live ones battery, rather you are letting the live cars alternator charge the dead cars battery. This can take a long time, especially if you have a Pug 106 trying to jump a V12 Jaguar (as I had once!). Leave it a good 15mins, then try again. If it still doesn't work, or it's not practical to try again, and you don't have access to another battery/charger or a volt meter, just call the RAC. You might want to read your cars manual re: immobilisers etc in case that causes an issue (usually it wouldn't stop the car cranking though).

[spikeyhead]

Andehh said:

Nope, the engine wouldn't even crank. Lights would flicker & die on dash and starter motor wouldn't catch on.

The car we were junping off a Saxo so hardly pumping with energy, same with the Ebay battery booster.

The fact the locks work & dash lights up as well as carPC turning on makes me think the battery wasn't utterly discharged so might be lucky. Any other comments would be appreciated!

I'll guess that you've got some poor jump leads, there are very few good sets out there. How long did you charge the booster pack before trying to use it? I think they usually want 14 hours charge before use.

[jagracer]

Check the earth lead from the battery to the engine is tight or put the negative jump lead straight to the engine. Check the jump leads are OK and the connectors on the leads are touching the battery terminals properly, I had one where the plastic cover was completely over the jaws of the clamp.

[andy-xr]

Andehh said:

Nope, the engine wouldn't even crank. Lights would flicker & die on dash and starter motor wouldn't catch on.

The car we were junping off a Saxo so hardly pumping with energy, same with the Ebay battery booster.

The fact the locks work & dash lights up as well as carPC turning on makes me think the battery wasn't utterly discharged so might be lucky. Any other comments would be appreciated!

Saxo battery is probably a bit too small to jump something same size or bigger off. Someone with a big diesel that doesnt have a battery hiding in the boot would be best option

[Ozzie Osmond]

spikeyhead said:

I'll guess that you've got some poor jump leads, there are very few good sets out there.

+1. In particular the clamps on most retail sets are not up to the job of allowing the necessary current to flow. The contact points are too small and the springs aren't strong enough.

[Mroad]

jagracer said:

Check the earth lead from the battery to the engine is tight or put the negative jump lead straight to the engine. Check the jump leads are OK and the connectors on the leads are touching the battery terminals properly, I had one where the plastic cover was completely over the jaws of the clamp.

+1
You most probably just had a poor connection. It sometimes takes me a few goes to get a good connection on the leads especially with terminals coated with anti-corrosion grease.

[giggity]

If you have to call out the RAC to get going - Do NOT buy a battery from them (stating the obvious)
It will be over priced and a cheap brand.

If you need a new battery go to Euro Car Parts or even better go to Costco and get the Bosch S5

[Pickled Piper]

Call the RAC that's what they are for. They will be able to jump start your car and also check your battery as well as your charging system. However, if they offer to sell you a battery check the price carefully. They have have a reputation for ripping customers off.

pp

[oldcynic]

Just get the RAC to get you started. Their technicians certainly used to be on commission for battery sales so they're reasonably likely to tell you it's knackered.

If you have a flat battery again for no good reason then your battery is probably knackered - check the output voltage when there's no load (ie disconnected from the car) and google for the correct answer - something like 13.2V but I can't remember exactly. Anything below 12V would indicate a failed cell in the battery.

[cambiker71]

varsas said:

How long did you leave the cars connected for? Usually when you jump start a car you don't try and start the dead car off the live ones battery, rather you are letting the live cars alternator charge the dead cars battery. This can take a long time, especially if you have a Pug 106 trying to jump a V12 Jaguar (as I had once!). Leave it a good 15mins, then try again. If it still doesn't work, or it's not practical to try again, and you don't have access to another battery/charger or a volt meter, just call the RAC. You might want to read your cars manual re: immobilisers etc in case that causes an issue (usually it wouldn't stop the car cranking though).

This sounds like your issue, try leaving the donor car running as mentioned above, getting an assistant to hold the engine around 2000rpm will help too, then after a few minutes charging try starting it again.

[jsg612]

Buy a new battery and replace it. It will only leave you caught out again at some point in the future. It's not worth it for £50 or so.

[CraigyMc]

andy-xr said:

Andehh said:

Nope, the engine wouldn't even crank. Lights would flicker & die on dash and starter motor wouldn't catch on.

The car we were junping off a Saxo so hardly pumping with energy, same with the Ebay battery booster.

The fact the locks work & dash lights up as well as carPC turning on makes me think the battery wasn't utterly discharged so might be lucky. Any other comments would be appreciated!

Saxo battery is probably a bit too small to jump something same size or bigger off. Someone with a big diesel that doesnt have a battery hiding in the boot would be best option

I'm surprised by this comment.

I always thought you jump started a car off the power of the other car's Alternator, not the other car's battery (this is why the live car is supposed to be turning over, while it's jumping the dead one).

Do you actually know what you're talking about?

C

[Ozzie Osmond]

CraigyMc said:

I always thought you jump started a car off the power of the other car's Alternator, not the other car's battery (this is why the live car is supposed to be turning over, while it's jumping the dead one).

An alternator will have a maximum output current of around 100 amps (in other words delivering roughly 12 volts x 100 amps = 1,200 watts). The current rises with engine speed and at tickover or low rpm it's unlikely to deliver more than about 25 amps (say, 300 watts).

The current drawn by a starter motor typically requires a battery which is able to deliver about 500 amps. 12 x 500 = 6,000 watts.

This is why the leads from battery to starter are fatter than the leads going to the alternator.

Having the engine of the other car running helps the jump-start process (voltage and current) but its alternator doesn't produce all the current you need to achieve a start. It also avoids the risk of ending up with BOTH batteries flat after extended cranking.

CraigyMc said:

Do you actually know what you're talking about?

Well there ya go....

[oldcynic]

CraigyMc said:

I always thought you jump started a car off the power of the other car's Alternator, not the other car's battery (this is why the live car is supposed to be turning over, while it's jumping the dead one).

No.

Use the alternator on the 'live' car to charge the dead battery for 10-15 minutes, then (depending on who you listen to) turn off the engine to avoid alternator damage before starting the 'dead' car. Once the other car is started the leads can be disconnected, although some suggest waiting a while to allow the voltage to build up in the flat battery and avoid upsetting that alternator.

The starter motor will draw several hundred amps (depending on the engine) so unless you've got huge jump leads with very large contact areas you won't get enough power down the jump leads, and you certainly won't start it off the other car's alternator. However the leads will provide additional current to bolster the starting process, combined with the charge which has been put into the dead battery.

Alternatively, as suggested repeatedly, pick up the phone and get a professional to do it. You've already paid for the service.

[Camaro91]

I didn't know you could get jump start leads that plug into the cigarette lighter... the current drawn from the starter motor can be in the double figures. I would have thought that would just take the fuse on the lighter circuit immediately?!

EDIT: unless they're just for charging, not for starting... which makes more sense

Edited by Camaro91 on Wednesday 29th December 17:22

[andy-xr]

CraigyMc said:

I always thought you jump started a car off the power of the other car's Alternator, not the other car's battery (this is why the live car is supposed to be turning over, while it's jumping the dead one).



C

I've jumped cars from batteries I've had lying around. No alternator required

ETA, I've also tried jumping a Focus from a Mk2 Fiesta. Interesting watching the rev counter jump around while cranking the Focus

Edited by andy-xr on Wednesday 29th December 18:19