Just replaced my original Varta (11/04) with an Energizer AGM from Sams. About $150. Perfect fit. The old Varta still seemed good, no codes but after sitting a few weeks it would crank a few seconds before starting, also the spoiler has gone up at odd times. Sams has an Energizer that is not an AGM for about $105.
If I understand this correct the AMG has a gel inside and won't leak, also a higher cold cranking amps and an AMG loses about about 1 or 2 percent of power a month while sitting up compared to a regular battery loses that much a day. Other brands also have AGM batteries.