Hi

Car has never given any problems in the nearly fours years I have had it.

Car driven over the weekend with no problems ( even the stop start worked on Saturday which is rare ), come Monday morning the car was completly dead (doors would'nt open no lights on the facia panel ). Called the RAC who found that the battery was only showing 4.2 volts, jump started the car and left running to charge up the battery until my charger would work. Locked the car Monday night fearing I would have the same problem the following morning, Tuesday morning the car doors opened and engine started as normal, before starting the engine I checked the battery voltage which was showing 12.8 volts.

Any ideas what would have caused the problem , I am sure that nothing was left on to drain the battery during the night.

Many Thanks

One of the car's modules probably didn't shut down properly.

It's often (but not always) the TCU.

The battery going flat will have reset all the modules and "rebooted" the offending module.

Thanks for your reply, could you explain what the TCU unit is ?. Is it common for a module not to shut down properly ?.

The only thing what happened on Sunday was torrential rain and partly flooded roads which caused a lots of spray.

Many Thanks

Telematics Control Unit.

It is the modem for the car, it is supposed to keep itself up to date. Ford rolled out an update which is supposed to prevent this.

It has its own battery and stays awake while the car is locked to operate remote locking. But if it crashes it can drain the battery.

It might not have been that module, but it is known to cause flat batteries. I had it happen to me when the car was about a year old.

Thanks for your reply , I will check the voltage each morning to see if there is any drain. The car is due for its four year service in `December and I will mention the problem to the dealer (unless it happens again before then ). Does disconnecting the battery for a few minutes reset all the modules and would this help in prevent a further occurance ?.

I also have a Maypole charger , when I connected it to my battery the LCD screen was red , I suppose this was because the battery voltage was too low. Does that mean that a Maypole cannot charge a battery when its flat?.

Many Thanks

Our resident expert on Maypole chargers @StephenFord, will I'm sure confirm that the charger will have no problems in recharging a normal flat battery whilst connected on the car.

Don't just randomly disconnect the battery for no reason. You can on occasions introduce other problems by doing that. Not to mention every time you disconnect the battery you have to reset all the windows for the one-touch operation.

It is important to make sure when you connect the charger that the positive lead is direct to the battery terminal and that the negative lead is to the chassis earth point, NOT the battery negative terminal. A good 12 hour overnight charge sorts most things.

Remember that your cars smart charging system is designed only to charge the battery to a maximum of 80% so it leaves very little room for the battery voltage to drop before you start getting problems.

The Maypole won't charge flat batteries.

It needs to see 7.5 volts before it'll charge a 12v battery.

4 minutes ago, TomsFocus said:

The Maypole won't charge flat batteries.

It needs to see 7.5 volts before it'll charge a 12v battery.

That is absolutely the stated specification for the charger, however, a couple of years back I did try it on a battery that had gone down to 6V, left it overnight, and it did coax it back into life, but I wouldn't rely on my experience, but if you've nothing to lose...

To be fair most peoples 'flat battery' is usually more than 7.5V

Anything less than 11.9V can easily be considered flat but still within the scope of many chargers.