Hi there,

I don't know if this is meant to be in this section of the forum as it a general question and not really specific to fords. I've been having a consistent problem with my focus where the battery needs a jump start around every 2 months. I've been racking my brain trying to think what could be draining it, and the only thing that is left on when the car is not in use is the black box/telematics box. I don't believe its the alternator as we've had it checked, and I don't want to invest in a portable jump starter if its just the black box. I don't know if anyone else has had this problem with black boxes or it's just me trying to grasp at straws.

Any advice would be greatly appreciated

Hi Telematics (Black Box) draw about 50 to 100mA when at rest. So if a vehicle was parked up and not used for a couple of weeks then yes it would drain the battery.

If you take a typical car battery and say it has a capacity of 56AH then that means (in theory) that the battery could supply 56 Amp continuously for 1 hour before being flat. Or to look at it the other way around the battery could supply 1 Amp continuously for 56 hours.

Just to keep the maths easy if your Black Box was using 100mA (= 0.1 Amp) then it would take 560 hours to run the battery flat.

Of course in real life once the battery voltage falls much below 11 Volt then you risk your car not wanting to start. Depending on how good a battery you have and how well it was charged when you parked the car will alter how long it is before your battery is too weak to start the engine.