Why does it take less time to charge with a MULTI XS 3600 with just 3.6A compared to my old 11A charger?
Your old charger starts to charge with a high current that quickly drops. In addition, a lot of energy is wasted from the charger in just heating the battery. A CTEK charger starts charging from a very low voltage with virtually a constant current up until the battery has reached maximum voltage. The charger then continues with a constant voltage until the battery is fully charged.