2011 Ford Focus battery going flat

[Welly]

My Dad's 61-plate Focus pez had been warning of a 'Low Battery' every now and then (if he sits in the car with the Radio on) and then yesterday he returned to the car and it was completely flat, no warnings beforehand.

I'm sure I've seen somewhere about Ford's 'Smart' Alternators which can go wrong and drain the battery? does anyone know anything about this? seems too new for the Battery to be at fault.

[Bailes1992]

Average life of a car battery is 5 years so it's highly likely it's failed.

If the smart alternators fail then usually you will get a battery light high in the revs.

[Welly]

Cheers, I'll speak to him about it, he only does short runs so it could be too much load going on.

My Volvo's still got its original factory Battery with a build date of July 2004

[steve_earwig]

Urgh, stupidly warm here today, goodbye snow, hello headache

No idea about "smart" alternators, I did read something somewhere on Onanist John (Volvo?) about alternators that don't actually do anything at all if the engine revs are too low but nothing there for fokus among the plethora of clutch and gearbox failures...

(if he sits in the car with the Radio on)

Is that with the engine running? If yes then maybe it's just not charging at idle, if no then maybe the battery just doesn't have it any more, like Sam says they don't last forever. That would seem more likely if the battery is dead flat. Remember this? viewtopic.php?f=3&t=6170&p=61391&hilit= ... ars#p61391

YOu could try charging it and see if it holds, get the engine running and see what the voltage is from the alternator. I guess it doesn't matter if you get it a new battery and find out it wasn't the problem as chances are it won't last much longer anyway.

Edit: A 10 year old battery? Swap it out before it leaves you stranded!

[Welly]

A bit of googling suggests this IS common, seems to be there's a high load with the car's 'Infotainment' stuff and short journeys, coupled with a dozy Alternator, and you can 'miss' important charge windows.....then you can find the car trying to 'catch up' for days. I guess the Alternator saves fuel by only jumping in when it's really needed.

My Dad has been sitting with engine off listening to Radio 4

[mjb]

Lots of batteries - especially lead-acid ones such as car batteries - really don't like being kept at anything but fully charged. Keep a battery partially discharged for any length of time and it's going to die quickly. In my experience death is often quite sudden.

From what I've read, it takes around half an hour of driving to replace the power used by the starter motor, so short trips are definitely bad unless you habitually use a trickle charger