75ZT Community

After 2 days unused, the battery on the V6 was down to 2V.
This is a fairly new Bosch item (earlier this year)
The Satnav shuts down correctly and nothing plugged in to aux sockets etc.

However, after charging the battery again it has now stood for 5 days and no problem.

Anyone any idea as to what is going on?

I am just having to make do the V8 until I am sure of the 75.

At the first 'fail' ("after 2 days") the battery may have been on its last legs due an un-indicated failure to charge. The inactivity (presumably alarm armed etc) helped it to lose the will to live. Standing for five days without running, and at max level, it could have retained sufficient charge to function initially. Suspect and investigate charging circuit.

Condolences on having to use V8. Any more phoney excuses would be gratefully appreciated.

Good thinking but it does appear to be charging OK as I have checked the voltage when running at 14.6V or thereabouts.

You don't know how hard it is coping with the noise and acceleration every day.

The alternator could be the culprit, Bernard. Recently I had a similar problem with my MG. With the engine running the voltage has been above 14V, yet the battery did not get charged. As a result there has been no warning light and the battery got drained while driving.

My battery went flat of it's own accord over three days a while ago, got it jumped off my friend's Nissan Quashqui, and it's been fine ever since. After the meet at Cosford it stood for two months without running and started first turn of the key, no problems. Which was a little confusing. But it's not shown any indication of a drain anywhere apart from the clock on the dashboard.

I'm so far from being a 'professional' in this as to be approaching amateur status from a southerly direction, but I believe there is no effect without cause. Instances where a magical anomaly is observed invariably mean either a Divine Intervention or a perfectly understandable failure which has not yet been explained. Come to think of it, pretty much the same thing.

If a static battery loses its charge over a few days the only cause can be a low state of charge to begin with, together with a minor drain. The efficiency of the battery may be tested by a 'leak' test following charging, rarely done with the advent of the cheap batteries available coupled with the relief when a boost charge appears to sort the problem. The low state of charge leading to the failure arises when our attention is elswhere because warning is not given. Idling in traffic
(with under-performing charging circuit) with powered ancilliaries operating (ICE, A/C etc)
will produce the cause which leads to the effect. When fully charged the efficient battery will last a surprising time without being re-charged until it fails again. A full electrolyte and leak test after charging may be the belt-and-braces choice.

All obvious I know, but sometimes we can get a bit too close to a problem.

You may be closer than you think, but I think your explanation is wrong. Remember the battery is basically a chemical reaction, so I'm not sure what would leak.

I too have had a couple of times when the battery is known to be low, that it then plummets in charge. Too much for just the normal drain to be doing it's work. Remember there are systems that wake up and shut down at various times, like when you open the door, or unlock the car. My theory is, though untested let alone proven, that something on the car doesn't shut down properly when the voltage is slightly low. So if the system wakes up, for example if another car is unlocked so the receiver 'sees' the signal but decides to ignore, then something stays awake causing the system to then drain the last remaining very quickly.

Funnily enough, it's my 1999 built V6 that seems to suffer from this, rather than the 2004 diesel.

Hmmm... very interesting. It's the usual problem with electricity - you can't see it! I'm sure my ham-fisted explanation isn't the whole story and I hadn't thought of whole systems activating on one signal. Chemical reaction yes, but is it not also a current storage facility similar in that respect to an accumulator?
With regard to the 'leak' reference: in my business I had to have my products and complete range of tools PAT tested annually to comply with then current law. The boffin that came to issue certificates would regularly test for leakage of current and one of his criteria was 'surface leakage of current from equipment and manufactured items'. I assumed it referred mainly to static current but could of course have been faulty wiring. This was all at mains voltage of course and the lower 12 volt system on cars would not be anywhere near as noticeable?

Would the rate of current dissipation from an uncharged battery increase at, say 2 or 3 volts?

Just had another thought. You mention the fault appears to affect only the 1999 car. Have you tried swapping the batteries over to see if it is repeated?

That's interesting.
However, today I have heard of another one with similar symptoms and the alternator was found to have an intermittent output. But this would not explain a drop to 2V, I think.

We are off to Spain in it in a few weeks time so obviously I want to get to the bottom of this fairly soon. (Or take a spare battery with us!)

Bernard, in your case it might be a combination. Mine takes more than two days to go down from well charged, but it seems to be either just a bit low, or have plummeted. I wonder if yours were a bit low due to intermittent alternator output, triggering this high drain effect at low voltage?

Hmm, I am changing the belts shortly so may well take the opportunity to swap the alternator out too.

Amp drain checks been done ?

Lates wrote:Amp drain checks been done ?

Not as such but the battery voltage is still slightly above 12 after standing for 5 days.

Started up fine and the alternator appears to be charging the battery.
I will run it around for a few days and see what happens.