Car clinic: Will the battery of my Mercedes C180 stand being left unused for six weeks?

Your motoring problems solved

Battery resized

Q. I’m planning a six-week trip, during which I intend to leave my 62-plate Mercedes-Benz C 180 parked on the drive with the security and electronic systems active. Will the battery run out of charge over that time? If so, is there a way to leave a trickle charger connected without sacrificing security?

TM, Worcester Park, Surrey


A. As your car is only about 18 months old, the battery should be in good condition, assuming you’ve been using the car regularly. The immobilisation and alarm systems take little power, which means that in this warmer weather the battery should retain sufficient charge to keep them running for six weeks. But it’s a stretch and I don’t recommend it, because batteries perform better and last longer when charged and discharged on a regular basis. Letting a battery go nearly flat like this can cause permanent damage.

One solution would be to arrange for a friend or neighbour to start the car once a week — or, better still, take it for a 30-minute drive. But this assumes you have someone whom you trust enough to secure the car after each use, and who is suitably insured.

If you can run a mains extension cable safely to your car without leaving your house insecure, you can connect a trickle charger. The CTEK MXS 5.0 costs £80 at, has a five-year warranty and includes several safety features — power is automatically cut if you connect up the wrong wires, for example. It clips easily onto the battery terminals without the need to disconnect the battery.

If you route the mains cable under the car and up into the engine bay, you won’t need to leave the bonnet ajar. I suggest you plug it in via an RCD (residual current detector — a sort of circuit breaker) for an extra measure of safety. RCDs cost about £10 at DIY stores.

Sunday Times Driving car clinic expert: Dave Pollard

Dave Pollard has written several Haynes manuals and has tested just about every car-related accessory

Search for and buy a used car on


Email your question to or write to Car Clinic, Driving, The Sunday Times, 3 Thomas More Square, London E98 1ST, with a daytime phone number,
your address and as much detail about your car as possible. We can’t reply in person, so don’t send original documents or SAEs. Advice is given without legal responsibility.