Hi, I had the same problem. I found these and they hold up well, they are extra heavy duty velcro straps. They come in several different lengths, but I normally cut them in half, use a soldering iron, and put a hole in the ends (the heat seals the edges of the hole and makes it stronger). I then clamp the ends down to my battery tray/box using large washers that have a rubber gasket (so they don't cut into the velcro). Or you can get one that is long enough to wrap completely around your battery. Just keep in mind that these straps are thicker than normal velcro.
http://www.mcmaster.com/
Part # 3955T72