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Large Electrical Power Drain


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Hi we have a 54 plate 1.4tdci +

If we don't drive the car every day the battery goes dead flat (ie if not used on Sunday wont start for work next day)

So far we have tried:-

- leaving car locked / unlocked

- boot bulb removed

- interior light switched off

- roof dvd def switched off

- new battery fitted (even though old one checked out ok ---- now used on mini digger!!!!)

- put volt meter on battery and removed each fuse in turn --- only one using any power was ironically marked up as 'battery saver'!!!!!!!

To my mind it must be something quite meaty to drain the battery to such an extent so quickly --- any help or ideas please.

Many thanks

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You make the assumption that the problem is a power drain -

But that may (very probably is), or may not be the case - perhaps the alternator is not giving enough output?

Or perhaps the car is used in a way that the battery is flattened and it does not get a chance to recover (short trips, lots of starting, heavy electric use)

Or the engine is difficult to start (faulty glow plugs, lazy starter),

I recommend you get a plug in LCD voltmeter -


and monitor/ record the volts, dayin, day out - eg, if you park up on Saturday, make a note of the voltage, then see what it is on the Monday, before you start it (and after)

After checking that, you could charge the battery on Sunday as a temporary measure

Is it a smart charge system and a silver calcium battery?

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Hi --- thanks for your thoughts;-

-the car starts really well in all weathers (if used every day!!!)

-the alternator gives a good output (checked with meter) and def charges battery as once car has been 'jumped' on monday runs all week with no additional charging (bare in mind it is normally totally flat)

-the car does a reasonable trip each time it is started and hardly ever does short trips (we live out in the sticks a bit!)

As you will appreciate we can aleaviate problem by putting car on charge at weekend but I would like to sort problem out if i can.

-My view (for what its worth!!) is there is a circuit remaining open that would normally shut down when car is switched off and it is quite a major system due to the speed of the run down? As mentioned initally the only open circuit (by fuses) is the one marked'battery saver' but obviously other items must run off this fuse --- any ideas

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Well, not a lot of people know this but on a modern car, there is quite a significant power drain as normal when the car is parked up, the central locking, can bus, bcu, and other things are "always on", some systems stay on a bit after the ignition is switched off

Sometimes its "borderline" and a little bit extra load is enough to drop the voltage low enough to make starting difficult - "the feather that broke the camels back" - that may be why it appears fine most of the time and there is a problem after an overnite lay-up

A modern cars' electrical system is complex with many components, there may not be a simple answer, - there are no additional electrical loads, like sat-nav, or a mobile phone charger, etc?

in the old days ypou might find a simple answer like the boot light was staying on, etc

The simple answer is to percieve it as a fault (that may be the case) or as an exessive load, - so to "fix" the problem you fix the fault/ reduce the load, or you could increase the capacity of the battery

The suggested low cost (about £3) voltmeter is a convenient way of knowing if the car will start or not, and to monitor the voltage over time

The drain is there all the time, so the battery voltage gets lower and lower, after an overnite lay-up, there is enough voltage to start the car, after 2 nights, the voltage has dropped too low to start the car, -


the voltage before / after the layup over Sunday is very important to diagnose the problem and to gauge the current drain - if you could let us know the voltage on Sat, (or when you park up for longer than overnite ) and the voltage on Monday (or just before you start the car after a longer lay-up)

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You could try taking a battery voltage reading when the car is parked up, then disconnect one of the battery terminals and measure battery voltage again to see if there's a noticable difference.

If you see the battery voltage slowly creeping up once disconnected that's another indication of there having been a load on the battery, it's just hard to quantify exactly how much without taking a current reading.

You could do this by putting a digital multimeter (with 10A capability) in series with the battery positive cable. If it maxes out the reading and blows the fuse in the meter then you've got a massive current draw, otherwise you should be able to get a current reading you can then compare with another Fusion owner. Only problem is that if you disconnect the battery it could in theory reset whatever is giving you the problem in the first place. Ideally you could use a clamp meter but these aren't cheap.

Course another option is to just disconnect the battery over a weekend and monitor it's voltage, just bear in mind that you should leave the battery for 24 hours after the engine has been run before taking a voltage reading, as when the engine has been run it puts an artificial voltage on the battery known as a surface charge. This decays over time or when you put a load on the battery, typically 1% of it's capacity (0.6AH for 60Ah battery etc)

I'd be curious to know what's a typical amount of current draw when cars are with customers - through production they are put into a factory mode, then transport mode to limit electrical functionality and help save battery life. Typical figure for cars at work is in the region of 10-20mA once shutdown in Factory mode - in what's termed Normal mode obviously all electrical toys are active and take longer to shutdown (or power saver relay to cut in) but I'd have thought they would still work to minimise current draws once power save has cut in.

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Hi Troy ... You mention 'power saver' relay .....if this was faulty or not activating as intended, am I right in thinking lots of the cars tech. Would be left active so maybe causing power drain?

Any idea of its location in car, and I will try and check its functionally?

Thanks for your thoughts


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There's a potential if this has failed then you could have some extra power drains.

Just spent half an hour going through a wiring schematic before remembering your issue is on a Fusion and not a Focus :rolleyes:

On the Focus the battery saver relay only covers the interior lighting, boot, footwells and so on, but I can't find a wiring schematic for the Fusion (or Fiesta) to see if there's an equivalent used.

Has anyone got a link for either of these?

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Hi Troy ... You mention 'power saver' relay .....if this was faulty or not activating as intended, am I right in thinking lots of the cars tech. Would be left active so maybe causing power drain?

Any idea of its location in car, and I will try and check its functionally?

Thanks for your thoughts


the power saver or battery saver relay is controlled by the GEM and often stays on for half an hour after the courtesy lights come on or the keyless entry is activated

In that time there will be a current drain but it should go away after a set time (like half an hour/ 40mins)

if you unlock the door or make the courtesy lights ome on (even for just a second) it sets the battery saver circut on for another half an hour (so it may just be you setting it of, or something else (like a fault) may be setting it off)

test the battery saver after 40 mins and see if the drain has gone down

let us know what the voltage is pre/ post layup - there will be a minimum voltage that the car will start with - with an LED voltmeter (like the one i posted a link to, costing £3) you will know if your car will start or not, before you try starting it (taking more life out of the battery)

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