Well this is a really daft question I was asked the other day, but to be honest I don't know the answer.

How long can a modern car battery be disconnected before ecu memory or key memory etc will be lost. Bearing in mind it has built in satnan, keyless entry, etc etc

 

Can you not buy a trickle charger.

 

Yes of course, but I was asked the question and thought I'd see if anyone new

 

I doubt there is one single answer.
It depends on each system in each Make/model.

But it doesn't matter as the manufacturers have allowed for this, there is a backup way to get in and start the car.

Search "Flat battery keyless entry" and see the many results.

 

Yes I know there are ways to get in and start the car in the event of a flat battery, but my friend has a rs500 focus that he has in storage with 9 miles on the clock, if it was me I'd get it out and drive it. But what he asked that if he disconnected the battery how long would it be before the vehicle would lose all it's memory as he plans to store it for a long while.

 

Answer to your question..dunno!


When cars are new many are supplied in 'transport mode', so a lot of the modules aren't active and draining battery power when the vehicles are stored/in transit.

Depends from car to car, some have fuses missing,or a simple switch on the fusebox, some need going on diagnostic machine to disable transport mode.

Can't think right now if possible on mk2 Focus, but on some Fords it was just a case of brake pedal on/off 5 times, hazard switch 4 times on/off, to disable it.

Whether you can enable it the same way I don't know, it's not something I've ever needed or been asked to do!

Had a weird one recently, mk3 Mondeo diesel, showing key not recognised (PATS light flashing fast), been standing about 3 months judging by how out-of-date the tax was. I didn't think they could loose key memory, expecting ECU issues through jump starting or whatever.. but I just re-added the key to the PATS and it started.

 

Thanks for that, I'm wondering how people store cars like these. I know people use battery maintainers but I'm not convinced, there must be other ways as battery's don't last forever

 

It shouldnt really matter if it's 60 minutes or 60 weeks, flat is flat.

If it's French though it'll probably fuck up with the battery in working order ! Probably better never putting a battery in one lol