New thread on my old starting problem.

[sgould]

This is getting very difficult to pin down. 

2007 9-5 Aero estate.

I have had sluggish starting, as reported elsewhere.  On Saturday I did a round trip of 65 miles with headlights on.

On Sunday afternoon the car started promptly.  Battery voltage before starting was 12.1 volts.  I went out for short drive in daylight with no lights on.

On Monday lunchtime I just measured the battery voltage and didn't go anywhere.  Voltage was 12.1 volts.

On Tuesday, I checked the voltage again at lunchtime and it was 12.05 volts.  Car started OK, but a bit slowly.  Short drive.  Went out again in the evening with lights on for another short visit.  Car started promptly both times.

This evening I went out in a hurry, didn't check the voltage, and battery was almost dead.  The engine turned over slowly, but not enough to start.  I went to get the booster pack out of the boot, but the key button did not work to open the tailgate.  I could open the tailgate with the door button and the indicators flashed three times. But the key remote button did nothing. So the battery still had some life in it.

I started the car with the booster pack and went out about 12 miles.  When I got to the destination none of the the remote key buttons would work.  Tried it a few times, but nothing. Lock switch by gear selector was fine.  Locked car with key.  Car started OK to come home.  Got home and my remote would still not work, neither would the spare key that my wife has.

But my wife mentioned that she had had problems with the other key and had to press it several times to get it to work.  So I think it lost synchronisation. I pressed the key button a few times and it seemed to resync.  Same happened with the other key.

I've had flat batteries before and I don't remember losing key sync when it happened.  So, am I thinking along the right lines in looking at TWICE?  Or has anyone else found that the keys lose sync when the battery goes flat?  I don't think it went completely flat because, although the engine wouldn't turn over, the lock button by the gear selector worked all the locks, so did manual operation of the key in the driver's door.

Tomorrow I will be trying to get to the bottom of it all, I hope it isn't raining... 

[Audax]

I forgot where we got to last time but the numbers you've given suggest the battery is dud and needs replacing.

[sgould]

The bit that's really puzzling me is the fact that both keys lost synchronisation even though there was enough power in the battery to operate the locks with the internal buttons.

Even if the battery lost all power during the engine cranking, would the keys lose sync?  I don't remember having a problem with that when I have disconnected the battery on previous occasions.

[sgould]

Had a bit of a play.

In car this morning checked battery voltage 12.3 volts.  Car started.  Moved it a few yards so it was on the hardstanding.  Sat in car and checked that the glovebox light was going off when the lid shut - it was.  I put my phone camera in the glovebox and ran a short video.

By then the battery was showing 11.9 volts.  Cranking didn't turn the engine over strongly enough to start the car and cranking voltage dropped to 4.4 volts.  Taking the battery to be power checked with a load tester.  My small electronic battery tester shows it as "Good - 52%"  Last week it said "Good 69%".

But I may have a secondary problem.  Once started with the external power pack, the charging voltage was 13.4 volts.  Last week it was 13.9 volts and the week before it was 14.1 volts.

We shall see...

[sgould]

Interesting.  My electronic battery tester said "Good - 52%". 

52% of 760 A is 395A.

The Halfords electronic tester said "392A - Advise Replacement".

So have a new Yuasa battery in place of the old Bosch battery.  Same rating. And a new 5 year guarantee.   I still had the receipt from 2011, so is was all done in 5 minutes with no quibble.  So a plus for the Halfords man and their guarantee!!

Battery voltage after a brief run is 12.6 volts.  Charging voltage is up to 13. 8 volts - still a bit low? - and the lowest cranking voltage was 11.6 volts.

We shall see if that cures the problem.  Looks as if Audax got the right diagnosis!!

[Audax]

Battery voltage after a brief run is 12.6 volts.  Charging voltage is up to 13. 8 volts - still a bit low? - and the lowest cranking voltage was 11.6 volts.

We shall see if that cures the problem.  Looks as if Audax got the right diagnosis!!

Those values sound right to me, I think that the alternator on modern cars won't spike quite so high as it's not good for the battery. If you turn off all the ancillary equipment you might find it goes a bit higher.

[sgould]

Thanks! I'll play a bit more tomorrow, if it stays dry.

[jmblack]

When my battery was playing up a bit recently I had the key synchro problem. It was as if the voltage had dropped below a certain level, but not so far as completely dead. New battery and no problems.

[phoenix]

Will, I should be along to the Redbourn meet tomorrow. I'll bring my clampmeter so we can take a look at charging currents

[sgould]

That's great! Thanks!

[sgould]

Figures from the battery this morning.

12.6 volts
Cranking voltage 11.1
Charging voltage 13.52

[nine-fiver]

Just been through a year of the same issue. Slowly dying battery. Weak alternator. You know how it all ends. After 4 call outs by the RACV (brilliantly patient operators!) their analytics said it had done a cell, and would not accept and hold charge. Calcium coated battery, less than 3 years old. But hammered mercilessly, with a dodgy alternator that wasn't putting out enough volts over an extended period of time.
Check the temperature of the line to the Positive terminal. If it is hot, really hot, then the battery is getting charged and not accepting it. Short trips exacerbate the issue of course. Try a cold start with the lights on. If it cranks then the battery is healthy enough. If not, it will fall over.
I was charging mine overnight using a 900amp charger, and it would only last a few days. And then fail. Again.
Installed a rebuilt alternator, that puts out 13.8volts with everything running normally, at idle. Static volts for the battery are over 12.7 so yours sounds on the unhealthy side.
Is the alternator the original one? 

[phoenix]

Took some readings yesterday... with as many things turned on as possible, the alternator was delivering 100A to the battery, but the terminal voltage was a little low at ~13V. Might be a regulation issue with the alternator or it could be resistance in the cable.