In November 2006 I left my 2003 Focus for four weeks. When I
returned, the battery appeared to be flat. I had the battery checked,
and it appeared to be OK, but I bought a new one as a precaution. I
am now in Spain for eight weeks, and a neighbour has been starting my
car weekly, letting it run to keep the juices flowing. All was OK
until last Sunday, when he phoned to say that the battery appeared to
be dead - a repeat of my November experience. I am no expert in these
matters, but this looks like a random current that suddenly drains the
battery in a week. Surely this would not happen unless something is
left switched on, which it isnt. I am returning in three weeks, and
would appreciate any advice. Thanks, Graeme
You might want to check the under hood or trunk light, if equipped. Try
disconnecting the ground cable over night, to determine if the fault is in
the battery itself. Better yet have a competent technician do a draw down
How long has your neighbour run the car for?
Modern cars do have a significant idle battery drain; the ECU memory, alarm
system and even the radio consume small amounts of current all the time the
car is parked. Many will run down in two weeks.
Starting the car will also obviously use some more. If the car was only left
to idle for 10 or 15 minutes, it would have done more harm than good.
If you intend leaving your car for long periods fairly frequently, you might
want to invest in a special type of battery charger designed for this
purpose. You can leave it connected all the time you are away.
The cost of this might be less than the cost of regularly relacing your
battery; the life of vehicle batteries is seriously compromised by being
left after deep discharge.
There is obviously something wrong with your cars electric
system. A car battery should last at least 6 years as rule of
thumb, even under bad conditions. I'd let check how much current
the car uses if anything is switched off?
Depending on the temperature self discharging might well be
higher then this.
Untrue, the Focus three-phase alternator is well capable to
deliver enough energy for almost all electric equipment together,
even if the engine is idle. With one exception, the heated
windscreen needs about 1000 rpm or it will suck the battery
Ever used a clamp-on ammeter to see how much Amps three-phase
alternator can pump into a battery even on an idle engine if the
Seconded, though you can save quite some money on your electric
bill if you use a timer and run it for 1-2 h daily. If you happen
to get one of the better ones.
Read what the OP has written. He left the car for four weeks with a
flattening battery! No car battery will last for six years if treated like
that; they are not designed for, and will not tolerate, being left after
Also note that the OP said the original battery was replaced after the first
incident *as a precaution*! It may not have failed prematurely at all!
I'm willing to bet the OP has *no* problem with his cars electrical system
Absolute rubbish! The drain of modern cars when not in use is so high (when
compared to vehicles of the past) that some manufacturers are having to
arrange for software to shut down things like alarms and keyless entry
systems after a couple of days. Have a look at the specification of VAG
I've seen a "new" battery that had a manufacturing date of six months ago
start a car easily.
Why do you specifically mention "three phase alternator"? All vehicle
alternators I've ever seen are three phase! In fact, old British
motorcycles of the 1960's used three phase alternators!
Assuming the OP's vehicle is petrol-engined, his alternator is capable of an
output of 80 Amps. This would not be available at tickover of course.
However, that output would only be used to balance the demand; there is no
way that the system would charge the battery at that rate! It would boil
before it was full charged.
The highest charge rate I've ever seen to a flat battery (*not* the total
alternator output to the vehicle), is 30 Amps. (This was on a much bigger
vehicle than a Focus, ans was not achievable at tickover.) If you assume
that the OP's near-flat battery was recharged for 15 minutes at 30 Amps,
and his battery was a mid-range 60 Ah one, at best only one eighth of its
capacity would have been restored. It is probable that the cold- start
would have taken more than was replaced.
On the assumption the the OP's battery was 75% discharged, work out what
current would be needed to fully charge it in 15 minutes!
No. I've only done it with a proper ammeter. A clip-on of the type typically
used to measure DC current is not a very accurate or reliable device.
Strange, I have been working as professional car mechanic at VAG
decades ago, we used a clip-on with a $$ Bosch meter for this
sort of thing. Worked great!
Anyway the best idea would be if the OP would let some
professional garage test his electric system, we can only remote
The focus alternator provides 14V/90A as rule of thumb it should
deliver 2/3 of this at idle engine, about 60A. Leaving the engine
run for 10 minutes idle once a week with no or very few things
turned on should be enough to keep it charged. Even if I agree
there are far better methods to keep a battery fit.
It would be good enough to give a guide as to whether an alternator was
charging or not; it is unsuitable for anything needing accuracy.
I worked as an industrial electrical technician for over 40 years, and I can
assure you that clip-on ammeters are not accurate. The place I worked for
much of that time worked to medicine licence standards. It was not allowed
to measure current using a clip-on if the results of that measurement would
affect the product. We could only use them for rough and ready fault
Nope, the best idea would be that the OP found out how long his car had been
run whilst he was away. If for less than 30 minutes/week or so, he should
ask his neighbour to run it for longer next time. Better still, as I have
said and you have agreed, buy a suitable charger.
Nope, the alternators for petrol cars are rated at 80A; only the diesels are
90A. An alternator won't "deliver" anything. It will respond to a load.
This is much more likely to be around 50% at idle. It certainly will not
charge the battery at anything near 60A; the regulating system controlled
by the ECU would not allow it. What do you think would be the result if it
did? Have you ever seen a battery that has been charged at much too high a
Even given your values of 60A for 10 minutes, and assuming that the capacity
curve was a straight line, (which is isn't), you would only replace one
sixth of the batteries capacity. To try to say otherwise is to deny the
laws of physics!
You were certainly able to see what happens with an uncharged
battery with it. Of course they can't be that accurate, but
showed at least what you would expect from the numbers of the
alternator, perhaps +10-20%. If it was OK.
I doubt the device you used was in the price range of the one I
Seconded about a suitable charger, it is in addition much more
ecologically then letting the engine run for 30 minutes idle,
which is btw not even legal anywhere.
I do not deny anything, but the mere fact that it was just not
run long enough. It should have been enough for just the single
start needed. The OP mentioned he had already replaced the
battery shortly on a 2003 Focus! Which makes me curious if there
isn't some additional problem?
Sure it might be just frequent deep discharge, which is very bad
for this kind of battery in any case. Again this leads to the
I worked for the second largest pharmaceutical company in the world. If
there was an item of test equipment that was useful to us, we got it...
Most of the test equipment was Fluke.
All of our equipment was purchased with calibration certificates; every
instrument was re-calibrated annually. If an instrument needed to be opened
to replace the batteries, it had to go back for re-calibration!
Where are you based Michael? It's perfectly legal here in the UK to leave a
car ticking over. If it's on the street the driver must remain with the
vehicle. If it's on private property, you can walk away leaving it running.
But that was four months ago, and as I have already pointed out to you, the
OP only changed the battery "AS A PRECAUTION"! If a fault existed it would
have been obvious long before now.
The battery would probably have continued to work perfectly well for a
number of years.
This could be the action of the ECU self protection system that is being
fitted to newer Foci. It is fitted to the Focus Cmax which came out in 2003
so it could be on your Focus
The theory is that if the ECU senses the battery starting to get low , it
switches on the headlights to make sure that the battery goes flat and has
to be recharged on a charger rather than jump started. There is evidence
that sometimes this circuit goes wrong and discharges the battery for no
I realise that this might sound strange but I have it on good authority from
an auto electician who works for Ford.
You will find references to this on FFOC if you don't believe me!
You can't just start a car and leave it sitting, it wont charge the battery!
All that has happened is that the battery has used significant energy to
start the car, and it's not really doing anything, just idling. A decent
drive once a week would be much more beneficial than your neighbour starting
it every day.
Didn't you research this before you asked your neighbour to do it?
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