I have 2 types of batteries:

http://www.hobbyking.com/hobbyking/s...dProduct=14991
At 139x46x26mm, they're a little long and wide. They fit but especially with the wires coming out the end they're a pain.

http://www.hobbyking.com/hobbyking/s...dProduct=17272
138x46x25mm, very minor difference but much easier to deal with. The battery terminals coming out the top is a huge plus.

Ihave velcro on one side and use the plastic tiedown for the other. I actually don't care much for the velcro.