ford focus battery problem

my hubby has a 2004 tdci 1.8 ghia focus, he works away for two weeks at a time and when he comes back the battery is flat we had a auto electrician look at it and nothing obvious was showing ,
the alarm and immobilisor are on all the time he is away , would they drain the battery ????? this is the second new battery in as many months , the alternator seems to be charging ok ,it starts every day when he is home after the initial starting with battery boost pack
any help would be appreciated ...thanks
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You probably have a parasitic drain on the battery somewhere, like a door switch, glove box switch, vanity light switch, etc. Usually the switch is stuck on and the battery gets drained. All anyone needs is a simple test light to help isolate the cause of the drain, but you have to know what you're doing. So when your auto electrician says "nothing obvious is showing" he means he's not going to figure it out for free if it doesn't jump out at him and bite him in the face. Can't blaim him, he needs to eat as well, right?
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You have a parasitic drain and most likely it is caused by your alarm. Try hooking the fcar up to maintainer while he is away on his trips. It will keep the battery fresh and is alot cheaper than buying a new battery every few months. Easiest thing to do though would be to just put a quick disconnect on the battery so that when he leaves, he can quickly disconnect it and no problems when he gets home.
To check for parasitic drain, get a Digital Volt Meter that also measures Amps. With the DVOM set to measure Amps (A=) and with the key off, take the negative battery cable loose. Put one lead on the negative battery terminal, and touch the other lead to the negative cable, or the engine block. If that meter reads over 50mA (mA=MilliAmps) or .05Amps then the drain is too high, and you need to disconnect the battery for long sitting periods. It doesnt take much to drain a battery completely with a decent drain on it, but it takes 100Ah (amp hours) to charge a battery back up to full capacity. Thats charging 1 amp for 100hrs. So if you have a 5amp charger it would take 20hrs to charge a battery back up to full capacity.
Hope this helps...
Ford Tech
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replying to Ford Tech, J.Zimmer wrote: Thanks for pointing me in the right direction.
I recently tracked the "parasitic drain" down to Microsoft Sync & Satellite Radio in my 2007 Ford Focus. Removed both fuses from the panel inside the vehicle, to disable those systems, and the eliminated the power drain completely.
Thanks again for the following past input.

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Using trhe same formula in the reply from Ford (capacity / charge rate charge time), the 0.05A drain would take more than 83 days (capacity / drain rate = depletion time) to deplete the same battery. If the battery is weak and cannot support the 0.05A load, then it will be dead over a long weekend of non-use. If the car can start when used daily, but does not start after 3 or so days of being parked, then the battery is no longer able to hold the charge, and the normal and customary parasitic loads are not the problem.
Pulling fuses will buy a couple of extra weeks because the drains are gone, but the battery will hold the charge for shorter and shorter periods, even with the static loads taken away.
If the person posting, it looks like J. Zimmer, has the factory battery in his '07 Focus, I'd suggest that the battery is no longer capale of holding a charge, and is screaming to be replaced.
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