As you can see, everyone is different OP. If you truly "need" flat-tops, you can't go wrong with Sony VTC4's (or VTC5's, but legend has it they can only be obtained by slaying the unicorn that lives in the belly of the dragon that lives in the belly of Moby D., the Great White Whale) or MNKE's, which are the primary choice of many sub-ohming fanatics. Quite frankly, any flat-tops are fine as long as they can handle the amperage you are pushing through your atty. Here's a chart with some basic battery info.
As for the charger, the one linked below is a wonderful option. It is cheap, durable, and stops sending a charge once the batteries read as "fully charged." Overcharging your batteries will diminish their shelf life very, very quickly.
http://www.amazon.com/NiteCore-Intellicharge-i4-Battery-Charger/dp/B007S9P3BC
Hope this helps, and good luck.
Edit: Just noticed the bit about rough terrain. I did you a solid and loaded four batteries into my charger (same as the one linked above), then proceeded to violently shake it. Two popped out, two stayed in. I'd say take your chances.