I primarily use velcro. I'm always impressed when I find that a model has a hatch designed around a battery, however. Like the Dynam 1200mm Spitfire. Or the Radjet. Or 1400mm Starmax J3. You literally pop the correct sized battery in, put the hatch on, and the hatch secures the battery in place right on cg.
Fitted hatches are nice but they limit your options. I use heavy duty velcro for everything electric, but I use additional velcro straps around my heli batteries. On my nitro planes I wrap the batteries in foam rubber and then velcro it in place.
I too use Velcro. But I use the 3M stuff from Wal Mart and other stores. The adhesive holds tenaciously like no other I've seen. Plus, the hook and pile of the Velcro holds fast even in not so stellar landings! Ha ha! I should know I've had some of those. I use it on every scratch build I do. Once I put a battery that was given to me in my F-22 that had some wierd pile on the battery and it came loose just before landing. After replacing it with the 3M stuff, no issues even though the battery is suspended hanging from the bottom flat portion of the fuselage.
You can see this happen and even hear the battery sliding back and forth in the plane on this video. I'm just glad it didn't get into the prop! Ha ha!