My 2010 also appears to have the original non AGM battery....I'll just replace it with like for like but the biggest that will fit in the tray and is the correct hight. I've found that fitting AGM on cars that did not have them as syd leads to problems...probably because they should be charged at a higher voltage than a normal lead acid battery..... the AGM one I fitted to my 159 only ever seemed to be fully charged after a go on the Ctek.....but was fine with a normal one.
You make an interesting point about the charging system of the car and compatability with an AGM battery if the original was VRLA 'wet'.
I also note that the CTEK has a different charging setting for AGM and the standard one never achieves that top green light!
And there was I also having second thoughts about the wisdom of going for a 'wet' battery, despite the fact my car is pre-Stop-Start, on the basis of markjay's 19 Sep 2020 post.
He points out that the Varta OEM battery may have been made by Varta but it was to a Mercedes spec and that same battery is unavailable from
anyone in the aftermarket other than Mercedes (including Varta Bosch), and will last 15 years.
So, his advice, to paraphrase, if not paying up for an actual Mercedes battery, was to get one from a trusted source certified to fit the car from another leading brand, i.e. as opposed to one nominally the same
technology as the original but maybe not quite up to par with the
original spec.
This would open up the possibility that, apart from lazy upselling, possibly on the assumption that all cars are now Stop-Start and need deep cyclic recharging capacity, the recommended batteries may just somehow be a 'better' spec, more comparable with the original, which AGMs certainly are - and of course we pay 60+% more for that!
Your point, however, is that not only might this upscaling be
redundant for anyone not driving like a postman in a wet battery OEM non-Stop-Start vehicle, but it might not get on with existing electrics not designed for higher AGM recharging voltages either.
Naturally, if one is routinely using a CTEK trickle charger anyway this may not matter so much, but may explain the need.
However, it would be interesting to get more input on that point before anyone with an older non-Stop-Starter makes a move to either a Varta F19 'wet' or F21 AGM.
I had much the same dilemma replacing a headlamp bulb last year, in that at least two generations of bulb tech had arisen since.
And, given that the native electrics would have to be fooled with a resistor to accept the latest low energy option, I just went with a like-for-like old tech pair of 'hot' bulbs.
