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Slow Battery Drain On 1999 Mk2 2.5 Mondeo


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Hard to know where to start, anything new or different recently? That's a starting point other than that it out with the meter pulling fuse and constant checking that battery drain, start with a 24 hour voltage reading from fully charged and then pull a fuse every day and check again, also get your battery load tested it could be faulty, I've just had a brand new battery that was faulty.

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The way that you write this it seems that you have decided that there is a spurious drain current that is flattening your battery over 7 - 10 days. If that is really what you mean, do you have some evidence (like DVM readings).

One of the problems with battery-going-flat issues is that it could be spurious drain, it could be battery faulty, it could be battery not being charged fully and it could be battery worn out (although that is less likely if the battery is relatively recent, but then if it is relatively recent but has been used hard/abused, which it could be if the charging isn't working correctly, then it still could be what is going on and, as pragmatix says, it could just be a one-off bad battery).

Given that those different failure types have different paths to pinpoint the cause any more information that you could give would be helpful.

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  • 4 weeks later...

Hello All

Time passes but I got back onto this one.

The battery is Ford, 590CCA, 5 Year Warranty, 3 Years old, I don't think it is the battery.

See attached pics:

1. Across the terminals - 12.37v.

2. Across the terminals - 12.33v.

3. Series to earth - 12.08v.

4. Series to earth - 12.20v.   

This would appear to show there is a drain of around 0.15v.

This was without the doors locked oralarm set, so with the alarm set it would probably be more than estimated 0.15v.

The battery flats from full charge in around 4 - 6 days.

1999, Mk2, 2.5, Ghia X Estate.

At this stage without ideas and leads and reluctant to start pulling fuses to see what circuit might be causing drainage the answer may be to book it into a garage with experience in these issues, who might go straight to the problem.

The only other point is that the vehicle is fitted with a Tracker:


As I understand it, the tracker is passive till either the vehicle is started or the tracker SIM is dialed, when it responds with data.

Any ideas appreciated.


MondyBattDrainTest (1).jpg

MondyBattDrainTest (2).jpg

MondyBattDrainTest (3).jpg

MondyBattDrainTest (4).jpg

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Thanks for the link...it looks to me as if the relay in that anti-theft system will discharge the battery in about 14 days, all on its own, so I'd try pulling that out and see what happens. (And then there is the rest of the anti-theft system, which will draw some current. It won't take zero current when idle, but it might be quite small...or not.)

9 hours ago, Vegaone said:

This would appear to show there is a drain of around 0.15v.

...that's not really a drain, so much as the voltage drop caused by a drain: the drain would be a current, and that's more difficult to measure. Well, it is easy if you have a clamp-on current meter/attachment, but you'd have probably mentioned it if you did.


If you go around the fuses (or the anti-theft sys relay) and pull them, and in doing that one of them makes a bigger difference to the battery voltage than the rest, then that is an obvious suspect. If just thinking about that doesn't give you some obvious inspiration (like 'it was the a/t system fuse/relay... I wonder what that could mean?') then connecting the DVM in current mode to replace the missing connection should allow you to get an approx current reading. If, multiplied by several days, that gets you anywhere near the Ah rating of your battery, that's probably the one. (Milliamps, divided by 1000 to give amps, multiplied by hours)



"The Battery is Ford, 590CCA, 5 Year Warranty, 3 Years old, I don't think it is the Battery."

The Ampere-hours number would have been more useful, in this case, and I can't quite read the text on the battery. And, bare in mind that the capacity will decline over life, and just to pull a number from thin air, after 3 years the battery may well be down by ~20 - 40% capacity, so to 60 - 80% of its 'label' capacity (or lower, if it has been 'abused', by heavy discharging, for example).


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Thanks for that.

I attach pics of the battery label, you may be right then, it could be the battery is expiring earlier than anticipated.

This fault does trace back from 2 years following the new Ford Battery installation, the original battery always fired up even though it was then 11 years old.

Pics attached, solution may be to take Mondy back to Ford before the Battery 56bf10ba4d044_MondyFordBattery(1).thumb.Warranty runs out, and have it changed.


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Contacting Ford we learned that the battery was 3 Years and 2 Months old, and the Warranty 3 Years, brilliant timing, and so was no longer under warranty.

Researching, we came across this Bosch battery with plenty of excess power:




So it seems battery manufacturers design the capability of the battery to expire soon after the warranty runs out, and calculate the maximum potential of the battery by estimating the maximum time the vehicle could be left at an Airport Car park while the owner is away on a maximum average holiday break of say 10 days, giving just enough remaining power in the battery to start the car on return for the first 2 Years, during which time the battery will have lost perhaps 40% of its power.

Thereafter, it is not some unknown inexplicable `battery drain` from the cars electrics, it is the battery which has lost sufficient power to make it effectively useless if the car is left for more than a few days, so the answer is don't hassle trying to locate a battery drainage, get a new and bigger battery, somewhere around 700 Cold Cranking Amps.




BoschBattAutomaticTransOil (1).jpg

Edited by Vegaone
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