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Me and my car - Mercedes-Benz SLK55

Which battery charger is best

Haynes interim digital editor, Rob Keenan, runs a Mercedes-Benz SLK55…


Like many a car nut, I've long had a thing for V8 engines. They tend to produce beautiful 'music' from their tailpipes and have dollops of torque - two terrific automotive attributes as far as I'm concerned.

But I live in a modern house with a predictably small garage, and needed a car that would comfortably fit in it. Not an easy task, because most V8 engines seem to be installed in large cars - just take a look at Euan Doig's Monaro.

Luckily, Mercedes-Benz made the Mk2 SLK roadster, and fitted it with a range of powerplants including its 'AMG 55' 5.4-litre V8, mated to a 7G-tronic seven-speed automatic gearbox. I love it.

How battery charger works

I tend to use the Merc SLK at weekends, and not even every weekend, so it can easily sit there in the garage for a couple of weeks before its next outing. During the first Covid-19 lockdown in the UK that extended to several weeks.

Naturally, most cars (and not just the latest models - the SLK is 15 years old) don't like to sit idle. The battery is in good condition but the car's alarm and its ultrasonic cabin sensors have a habit of flattening the power pack within a couple of weeks.

So I bought a battery charger and maintainer/conditioner, which is designed to stay hooked up to the car for long periods. You simply attach one lead to the battery's positive terminal, another to the negative terminal, plug the unit into a nearby mains socket, turn it on, wait for a beep and press the start button.

You can then close the bonnet and lock the car - the unit is small enough to sit within the engine bay but I leave it sitting at the base of the windscreen, so I can see the battery's status at a glance.

Read more about how to maintain your car while it's parked up for longer periods.

why battery charger not working

It automatically detects your battery's voltage (12V in the case of car batteries, 6V for some motorbikes) and the simple display will even tell you if you've got the cables the wrong way round.

This is a trickle charger, so isn't much use if you need to get a flat battery going in a hurry - it'll probably take a couple of days - but it's perfect for my needs and will extend the battery's life.

Popular battery conditioner brands include Noco, CTEK and Optimate, but mine's AA-branded and cost less than $60.