Charging battery when car laid up for winter

[RonA]

Hi All
My Z3 is currently Sorned and under a cover in the garage for the winter. As per the handbook I've disconnected the battery negative terminal and connected a smart charger to the battery. Is this disconnection of the battery absolutely necessary, I've run a TR6 as a classic for a number of years and in the winter I leave it with the battery connected to the car with the smart charger on it and haven't had any problems, or do the electronics of the Z3 not appreciate this treatment.
Ron

 

[andyglym]

Hi All
My Z3 is currently Sorned and under a cover in the garage for the winter. As per the handbook I've disconnected the battery negative terminal and connected a smart charger to the battery. Is this disconnection of the battery absolutely necessary, I've run a TR6 as a classic for a number of years and in the winter I leave it with the battery connected to the car with the smart charger on it and haven't had any problems, or do the electronics of the Z3 not appreciate this treatment.
Ron

Left mine connected with a C-TEK on the go for ages over a 3 year period on and off, no issues.

 

[Pingu]

It could make a difference as an alternator supplies an analogue voltage that is very smooth, modern battery chargers supply a digital voltage which is spiky. The size of the spikes is small, but it depends on the sensitivity of the electronics in the modules. I would expect BMW electronics to be robust enough to cope with the spikes, but I always work on the "better safe than sorry" principle and only charge a disconnected battery.

 

[Nodzed]

Always leave mine connected with a C-TEK.

 

[abh29]

I just use the connectors under the bonnet,but do ensure the battery vent is OK.

 

[RTV]

I don't see anything wrong with using a trickle charger with the battery connected and I would use the connectors under the bonnet.

Doubt that charging a battery will have a negative effect on dormant electronics, if anything a modern quality trickle charger will be better than the old school voltage regulator on the alternator.

Nothing wrong with disconnecting the battery and charging it directly, unless you have an alarm. Doing that for a long period of time will drain the alarm battery and you might have issues after having to resync the remotes, etc...

I'd still recommend running the car for a few minutes at least once a month or every other week, not necessarily to charge the battery but to avoid issues in the fuel system. Modern fuel is not great at sitting still for long periods of time. Maybe even move the car back and forth a little bit to move the brakes too... specially if the car sits outside.

 

[Devon Z]

I leave the battery connected and have the smart charger fly lead plug fitted and plug in the charger periodically, I prop the boot floor panel open. I left a previous smart charger plugged in all the time and it went faulty and overcharged the original battery.

Used to start and run periodically also but just felt it filled the exhaust with condensation so it can corrode from the inside.

Anyway soon be March…………..oh had snow last March

 

[RonA]

Thanks for the replies, I think I'll just leave it as it is for the rest of the winter and next winter I'll leave it connected.
As a matter of interest the advice for running laid up cars used to be either take it for a 20 mile run or don't run it at all, cold engines produce a lot of acidic condensation, this was the advice for 'classic' cars but it would seem sensible for more modern cars as well.
Ron

 

[Fender2004]

Used a Ctek battery analyser/charger for over 10 years now on my Z, I always leave the battery connected to the car and never had a problem.

 

[motco]

My Z is charged every month with the battery connected. The only problem I had was when I didn't charge it and the battery went so low that the alarm went off.

 

[MarkLG1973]

I’ve just hooked up a little Noco Genius 2 amp charger to mine. Amazon had them on offer at £35 a couple of weeks ago.
Always used to leave my bikes on trickle over the winter.

 

[Mr H]

My Z is charged every month with the battery connected. The only problem I had was when I didn't charge it and the battery went so low that the alarm went off.

Was that with the alarm set? I ask because I've laid up mine unlocked so the alarm sensors don't drain the battery.

 

[Je55rfc]

I leave my smart charger on all the time. Car always bursts into life. I run it every week a few miles to just keep my eye on everything.

 

[motco]

Was that with the alarm set? I ask because I've laid up mine unlocked so the alarm sensors don't drain the battery.

Yes, Mr H, the alarm was set but it took a good few weeks to get to the alarm going off state. I put a charger on it and left it for a while, then switched on the ignition to see whether I was going to have to rummage in my files for the radio code while it was charging. The radio was fine but the instrument cluster was damaged and was showing only EEP and a number that I forget. It needed a replacement coding plug to get the odometer, tachometer, and (if I recall rightly) fuel gauge to work. The speedometer was working but reading high. I don't know whether the damage was due to the battery going flat or to me switching the ignition on with the charger still charging a still severely depleted battery. Chargers are pretty crude and electrically 'noisy' which would normally be smoothed by the electrical 'mass' of the battery but with a poorly charged battery that smoothing could have been absent.