I just started using 5S (18V) batteries which takes about 1 hour to charge at home from 120V AC input. In the field, using 12V input, it is taking 2 hours to get charged. I am using a Triton charger which says it charges up to 6S. With 3S I can get the same charge time at home and in the field. Seems to me that using 12V to charge a 18V battery is the problem. Is that right? Thanks. Alex