Why does my radio cut out after a few minutes with the engine off?

I have a Ford Focus. The manual states that with the engine off, I can listen to the radio for one hour. I can't, it cuts out after a few minutes. This seems to be a problem in general. Is this something to do with the battery, which may run down?

Asked on 30 October 2017 by David Hunt

Answered by Honest John
Modern systems are designed to shut off quickly to minimise drains on the battery because recharging the battery via an engine driven alternator uses a lot of fuel. If the alternator is regenerative (only works on the overrun) then it will not charge the battery adequately after a significant drain from something like a radio.
Similar questions
My battery went dead as I left my lights on. I was successful in jump-starting the car but now my in-car stereo is totally dead and there's a flashing red light on the stereo, which I guess is the alarm/immobiliser....
I have just replaced my Citroen Xsara Picasso with a new Citroen C3 Picasso HDI VTR+ (influenced by your review). I am extremely pleased with it apart from one niggling feature - I can't keep the radio...
I'm the happy owner of a 2013 Toyota Prius. I'm leaving the UK for two months in winter and wonder what actions you recommend I take with leaving the car on the drive? The longest I've left the car unused...
Related models
Relaxed but still enjoyable to drive. Flexible 1.0-litre EcoBoost and 1.5-litre TDCi engines. Interior improved over old Focus. Useful safety and convenience technology.
 

Ask Honest John

Value my car