If they fly well with that battery then stick to it. A 1650 sounds a little big (and heavy) for a slow stick, but if it works it works. As for chargers, any lipo capable charger that does balancing will work. I'll suggest getting one that also cycles so you can verify the capacity of new packs and test old ones to make sure they are still good. That little feature has saved me a couple of planes over the years, so it was well worth the investment. Dymond RC has an AC/DC charger that will serve you nicely.

http://www.rc-dymond.com/index3.php?productID=1873