I put an Exide Edge AGM battery in my 2003 Boxster because it works great in the cold (it gets really cold here, -20° F or lower) and I sometimes leave the car for weeks at a time in winter. I either disconnect the battery (I remove the frunk latch first), or I leave my CTEK charger hooked up. No problems and both the battery and charger work great! When the 2 batteries in my boat and the 2 in my diesel truck wear out, I will buy AGMs for them too!
Also, I love the blue color!
Battery Chargers - CTEK Battery Chargers MUS 4.3 POLAR