I'm in the UK. Car is 1.3 litre.

QUESTION (1) I know this may not be the best way of doing it but, in
theory, if a car battery got flattened by leaving the headlights on
then why would a fully charged second battery attached in parallel
to the flat battery give almost no help at all?

It's was almost as if the second battery lost nearly all its charge
to the flat battery.

Can someone explain what is happening with the battery charge
please.

QUESTION (2) If that's so then, to get the car started, is it
absolutely necessary to put a charger on the flat battery which is
in the car?

beccy wrote:
the booster battery may have been flat? Was it one of those portable
emergency start ones? The battery in those is tiny and rarely last more
than a year. Additionally the cables and connectors are often quite
insubstantial.

Assuming that the battery booster pack you are trying to use is in good
condition then it is necessary to connect the booster pack correctly and
then leave it for about five minutes to transfer some charge into the flat
battery. Then try and start it.

In article <Xns9CA4517B8AA07F3QA2 (AT) newsfarm (DOT) iad.highwinds-media.com>,
beccy says...


2) The flat battery presents a high load to the second battery.

Far better to to use decent jump leads and possibly remove the earth
terminal on the flat battery until its running then replace without
turning off the car, assuming that's an option.

--
Conor
www.notebooks-r-us.co.uk

I'm not prejudiced. I hate everybody equally.

In article <Xns9CA4517B8AA07F3QA2 (AT) newsfarm (DOT) iad.highwinds-media.com>,
beccy <no (AT) not (DOT) here> wrote:
If the second battery is good it means the connection between them isn't.
Most jump leads are incapable of carrying the full starter current. Ones
which can cost upwards of 50 quid.

If the battery isn't permanently knackered through being run totally flat,
another car connected to it and the engine run for a while might then
charge it enough. But an overnight charge with a charger is a better bet.
Lidl have some decent ones in at the moment for only 14 quid. Small enough
to keep in the car.

--
*Go the extra mile. It makes your boss look like an incompetent slacker *

Dave Plowman dave (AT) davenoise (DOT) co.uk London SW
To e-mail, change noise into sound.

beccy wrote:
Jump leads not making electrical contact. Some cheap ones have
insufficient metal in the plastic jaws and I've come across ones where
the rest of the plastic prevents metal to metal contact. Get a torch and
take a good look when you have them 'attached'. It's probably not
connecting ...

--
Adrian C

On 10:05 14 Oct 2009, Dave Plowman (News) wrote:

The jump leads have worked well in the past but they're not £50+
leads! Maybe this time the spare battery is having to provide
even more power than the times in the past.

"Pernanently knackered through being run totally flat"? Can it be
permanent? Is there an simple way to test this without going to
a garage?

On 08:26 14 Oct 2009, Mrcheerful wrote:

The booster battery was a proper charged up battery and not part of
a special emergency "unit".

I'll try it with the five minute arangement.

On 14:18 14 Oct 2009, Adrian C wrote:

I wondered about the area of contact because the clips had a sort of
lipped shape on each surface which meant the contact area was a
metal edge. IYSWIM. It didn't seem much to me. But if the area is
too small then wouldn't the jump lead clip get hot where it did make
contact?

beccy wrote:

Halfords, if you must, but they'll rob you blind for the new one...

beccy wrote:
then probably the jumper cables were a bit on the weak side, so a connect up
for a few minutes should do the job.
It is quite possible in emergency to jump start a car using thin bits of
household flex, just leave them connected for half an hour or so (then
remove the cables) and enough charge will have transfered to start it up.
They even make a dedicated jump start device that just plugs into the
cigarette lighteres of the dead car and a good one, you leave those
connected for about twenty minutes till the light goes green and away it
should go. Cigarette lighter circuits can only carry a few amps in any
case, so it is all done by transfer over some time.