This evening I tried to unlock my Slk R171 350 and nothing happened. Tried the spare key and still nothing. Released the manual key to gain entry into the car and tried to turn my key but the igition would not respond, I mean, the key would not even turn over. Could this be the battery you think?
If so the battery, I was thinking of using my Halfords battery charger on it. Would I need to disconnect the battery links first or can I connect the charger upto the battery with it still hooked up to the car and charge it that way?
Also, would charging the battery ruins any of my audio, sat nav settings?
Depends on the charger mate, if its smart enough it wont go overboard on the voltage but to be safe you might want to disconnect it anyways, it wont do anything major to the car you will just need to reset the windows and the clock if you dont have COMAND
I think what DansSLK is saying is that some chargers have electronics or other mechanism to detect when the battery is fully charged and stop charging. Many cheaper chargers will continue to try to charge the battery after the battery is fully charged which is not good for the battery.
I would not expect charging the battery to cause a problem with the electronics unless something is seriously wrong with the charger. The battery is charged by the alternator each time you run the car. You may have lost nav and radio settings because the battery voltage dropped before you charged the battery.
Are you sure your battery terminals are clean?
As for higher ratings on the battery, my experience is that you are pretty much limited by the size of the battery to something close to what MB put in the car when it was new. MB puts in a pretty good battery from the factory.
I have 3 bikes and an SLK in my garage, most of which don't get used through our long winter. Each one is connected to one of THESE. Every time after I take a bike out or drive the SLK, I'll hook it back up. It's max charge rate is only 750mA so if the battery is flat, it would take forever to charge it up, but it keeps a 'fit' battery fully charged, and it can be left connected and switched on indefinitely. It's 'intelligent', so it wont ruin the battery. On the bikes, I use the 'eyelet' cable permanently connected to the battery, and I've placed the socket in a convenient place so I can just connect the charger without having to open/strip down anything, on the SLK, I use the supplied croc clips, and just pop the hood, connect one clip to the 'shock 'turret'' bolt and one to the +ve terminal under the red flap/connector thingy adjacent to it. Never had a starting problem with any of them yet.
Sorry DanSlk, forgot the finish my comment... In some previous posts you've mentioned how to reset the windows which I should be ok with. However I do have command therefore would there be any other settings I'd need to re-establish?
It all depends on the state of the battery at the time you hook it up to the trickle charger.
I use the Battery Tender brand, which I think works the same way. With a reasonably functioning battery, it takes about 2 hours for the trickle charger to give me a flashing green LED (indicating about 80% full); this is the rapid charge mode and the charger has now switched to trickle charge mode.
I usually connect the trickle charger at night on a weekend, at which time the green LED is flashing; by morning, the green LED is constantly lit, indicating a 100% charge and is on maintenance mode. This is prolly another 6-8 hours after reaching the 80% mark.
I did have one incident where I discharge the battery down to 11 volts, perhaps less (considered no power by the electronics in the car), and it took roughly 8 hours to get to the 80% mark and another 10 hours to reach the 100% mark.