What's likely to be wrong with this car?

Here are the facts:
1. The car is used once or twice a week, mostly for short trips.
2. Nearly every time we use it, the battery is too dead to turn the engine over and it needs to be charged. In fact it's so dead that even trying will produce nothing but a click and drop the voltage across the electrical system so low that it resets the clock.
3. After 20 minutes or so of charging, it'll start without difficulty (it's only a 1.2l engine).
4. Alternatively, a quick push will do the trick.
5. If it has just recently been on a long drive (in the previous day or so), or has been used once that day already, it will start without problems, though.
6. More than once recently though I've stopped the car for a few moments after driving several miles, and will find that it doesn't start and needs a push to get going again.
7. It's getting worse.
8. The battery is fairly new.
I'm assuming that the problem is the alternator failing to charge the battery properly, but no. 6 is a puzzle to me.
Thanks,
Daniele
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On 03/03/2017 18:59, D.M. Procida wrote:

I was going to ask if you had access to a DVM but on reflection it sounds like an intermittent fault.
Is this car of an age when they were fitted with an OBD connector? If so then a pod connected to either a laptop or a phone will give a continuous voltage reading.
It's not a VW is it? The reason I say is a friend had a similar problem to do with updated software and a subsequent current drain.
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On 03-Mar-17 6:59 PM, D.M. Procida wrote:

Could be the alternator, but I'd double check the battery connections and the earthing from the battery to the chassis. Could also be a starter motor problem, check the spade connector terminal on it.
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No if it were the starter the clock would not reset.
Really needs to check the drain when nothing should be going on. Care needs to be taken here as taking the battery off line for too long can bugger up the radio coding.
Brian
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If the current drawn by the starter motor causes the terminal voltage to drop too far (eg due to high internal resistance of battery or its contacts) then it will drop below the threshold that the clock needs to make it work. That will reset the clock.
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On 03/03/2017 18:59, D.M. Procida wrote:

Something is discharging the battery. Either the battery is duff and is discharging itself or there is an electrical fault which is drawing current from the battery when the car is parked.
To find out which, leave the car overnight and then measure the battery voltage. Chances are that it will have gone down a lot. Then charge it and run the car and then disconnect the battery before leaving it overnight. If it has still gone down, the battery is duff. If it hasn't, you need to investigate the 'leak'.
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On 03-Mar-17 8:01 PM, Roger Mills wrote:

That wouldn't explain number 6.
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On 03/03/2017 20:03, Joe Bloggs wrote:

A few miles on a uncharged battery results in a still uncharged battery
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On 03-Mar-17 8:23 PM, alan_m wrote:

Depends how many miles and whether or not on those specific occasions the battery was actually 'uncharged' to start with - and he/she did say 'several miles'.
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On 03/03/2017 21:02, Joe Bloggs wrote:

Several miles in winter when headlights tend to get used more may not be enough to restore the energy taken from the battery to start the car.
A cheap DVM will show the state of charge of the battery.
Checking battery voltage with and without the engine running will show if the alternator is performing.
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On 06/03/2017 08:57, Martin Brown wrote:

Assuming there are no poor connections the charge rate won't vary much with the load from lights etc. The alternator maintains the same voltage irrespective of load. The alternator is more than capable of powering the lights, heater motor, etc, and also charging the battery.
I drive a vehicle with digital ammeters and I observe this fact frequently. I turn the headlights on, the voltage and charge rate dip down momentarily, then they resume their previous position.
The idea that you can't charge the battery if you have the lights and the heater blower on is a hangover from the days of dynamos. They had a max output of, typically, 22A, and SFA on tick-over. A modern alternator will produce 20A at tick-over and over 80A when the engine is running normally. The alternator in my 20 year old motorhome will power a 24V 45A microwave and still charge the battery at 20A, power the headlights, etc. (Yes, we use the micro when we're moving)
Bill
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when I fitted an alternator to my Anglia, the extra load was too much for the pressed steel pulley which broke, I had to buy a cast one - which Ford were able to supply.
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from KT24 in Surrey, England

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I've a feeling many car makers now set the idle speed rather higher than it need be purely to provide enough output from the alternator.
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On Thursday, 16 March 2017 00:45:14 UTC, Dave Plowman (News) wrote:

Drivel. The pulley on alternators is smaller than dynamos. The alternator performs better because it runs faster. It can run faster because there's no commutator.
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The battery on both those occasions was charged well enough to start the car.
Daniele
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message wrote:

That does suggest that the battery isn't charging after it has started the engine and during the subsequent running - either because the alternator/charging circuitry has failed or because something is drawing a large current so the alternator cannot supply sufficient current both to supply that load and at the same time replenish the battery charge that has been taken out during starting.
I'd suggest:
- If you can manage without the car for a day, charge the battery using a battery charger and then leave it for 24 hours without being connected to anything: this will eliminate self-discharge.
- If you have an ammeter that can measure large currents, connect it in series with the battery in the car with a) the ignition and everything else switched off, b) the ignition on but engine not running. DO NOT LEAVE IT IN PLACE WHEN YOU START THE ENGINE because the starter motor current will probably blow the ammeter or fry its leads. If there is a significant spark when you reconnect the charged battery (without the ammeter) then that suggests that a large current is being drawn, so maybe it's not wise to use the ammeter in that case.
- Measure the charging voltage (voltmeter across the battery) when the engine is idling and when it's revving at 2000 rpm. Certainly in the latter case you should see around 14V - higher than the voltage without the engine running.
- Measure the battery voltage with the ignition on but the engine not running - does this cause the battery voltage to fall below the no-load voltage of about 12V?
- Get the battery tested at a garage or at Halford's.
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On 04/03/2017 12:02, NY wrote:

Some Jap cars have a 15V alternator output. Doesn't seem to hurt the battery and the charge rate is better. Probably blows bulbs though.
Bill
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On 03/03/2017 18:59, D.M. Procida wrote:

Several miles isn't enough to charge a battery especially this time of year when you may have the heated front/back screen operational and/or driving with the lights on.
My guess that something electrical isn't switching off. A friend once had similar problems and found the the tailgate switch for the light in the 'boot' had failed and the light was permanently on - only found when the rear parcel shelf had been removed and the light could be seen at night.
Try buying a voltmeter that fits in the power socket / cigarette lighter It should show 14+ Volts when the alternator is charging the battery (perhaps after a good few miles of driving and with lights and screen heater off)
Ebay listing taken at random
https://tinyurl.com/h63p4am
OR
http://www.ebay.co.uk/itm/Hakkin-2-in1-Car-12V-Cigarette-Lighter-Plug-LED-Dual-Digital-Voltmeter-Tester-/112266184734?hash=item1a2396081e:g:uX8AAOSw241Ydwg-
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[12 lines snipped]

And fucked. Buy a new battery.
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On 03-Mar-17 8:09 PM, Huge wrote:

You might be right, but is that the only way you're able to express yourself?
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