My boss has a 2010 focus Titanium 1.8 petrol which randomly likes to drain its battery. Today he drove it about 5 miles, parked it on site, moved it around a couple of times and then when he came to drive home tonight it was flat. A quick jump start from my focus got it going.

 

The car also seems to turn on its auto headlamps if the battery is low (even with the switch in the off position), compounding the problem.

 

Now, I have two suspects, one is the fact the battery is a Ford Silver Calcium one (so probably 8 years old) and secondly the radio has been changed for an aftermarket unit (IIRC this can cause the Bluetooth unit to stay on and cause a drain?). Am I right in thinking the best thing to try first is a new battery before I try and get the Bluetooth module out?

Does the mileage display stay on after you've locked the car, it should go off after 20 minutes, mine was staying on which eventually drained the battery, the fault was the bluetooth module not shutting down which is behind the glovebox, I just disconnected mine and all was fine.

It does seem that the instrument cluster is shutting down correctly after locking the car, so it seems its the battery at fault.

Is it a big job to change the battery on a MK2.5?

39 minutes ago, rhyds said:

It does seem that the instrument cluster is shutting down correctly after locking the car, so it seems its the battery at fault.

Is it a big job to change the battery on a MK2.5?

10 minutes if it's a model where the airbox needs to come out to get access to the battery and 5 minutes if not.

My Dad had an issue with his Focus constantly draining battery. Turned out to be an issue with the ignition (wasn't a start/stop button but a fixed key type thing) i believe there is quite a common fault with the focus (sorry if im wrong and im sure someone more technical can advise further).