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1, Replacement of battery:
I got problems to start the engine when I have not used it for a week or so, find that the battery was out of power, it looks new but something wrong with it. And it was also only a 60 Ah capacity, it should be a 74 Ah battery. I bought a new 74 Ah Bosch battery and luckily it was a 25% discount these Christmas days and a three years guarantee. After a week without use I tried to start the engine today with minus 13 degree Celsius outdoor temperature, no problem, it started direct!
The battery is placed on the right side, just below the front window. Always loosen the negative battery terminal first and pull it away from the battery. Underneath the battery it's common with corrosion, clean and put some rust protection on it and your car will last longer.
I have found even with the new battery the car can be difficult to start when it had not been used for a couple of weeks. About three weeks in summer and two or three days in winter when it's cold. After have reading on internet for the corresponding Mercedes SLK I found that they say that Mercedes had problems these years. The electronic devices take too much current. Maximum shall be 0.09 Ampere or 90 milliamp.
I connected an Ampere meter on the minus pole of the battery in serie with the cable. I set the Ampere meters range to 20 Ampere, it take a lot of current the first seconds.
Direct when connected it takes 0.72 Ampere.
After about 30 seconds the current goes down to 0.27 Ampere, that's too much, but I think I didn't waited enough long time to let the current go down. With a current of 0.27 Ampere the battery shouldn't last for at most a week. I will measure it up more carefully later, but I don't think there is any problem with leak current, I just have to live with this because it's in the construction. They also give the recommendation that always have a fresh battery, replace every three years. The battery life time will goes down if it's deeply uncharged. From now and on I will always disconnect the battery or take it out and set it under charge if I will not use the car for a couple of weeks.
My friend Robert found a good link how to find this kind of problem:
Two years after I replaced the battery I was once again having problem to start the car. Battery looks to be in top condition. Maybe there is the problem with the current drain of the battery when in rest. I take a deeper look at it on next page.
New battery once again:
The times goes on and now it's 4.5 years since I replaced the battery. It can now just after a few days not crank the engine when the car has been parked. The battery should have last longer, but the cars relative high standby current maybe lower its lifespan.
This time I bought a different battery, it's a Silver-Calcium battery, I have no experience of it, but must try something different. It has a 78 Ah capacity to compare with the standard 74 Ah I had earlier. It can deliver 660 Ampere at -18 degrees Celsius during 30 seconds. The earlier one could deliver 680 Ampere. The dimension of it is the same: 275 x 175 x 190 mm and weight 17 kg.
It has a built in indicator of the battery's condition.
Green color means good condition, it's new !
Anyway, I set it on charge before I install it in the car, my car needs all power it can get.
Have used the car now for a couple of times, it behave as it should but it's not very cold anymore, about +10 degrees Celsius.