bowlofsalad
100 kW
If there is anything that is perfectly made for your battery, I'd be surprised and I surely don't know about it. As it's been said, that means you are going to have to make the battery box yourself through modifying some other purpose box. The options are many. There are many kinds of boxes made for carrying all kinds of different stuff, some are water proof, some are not. The real problem in my mind comes into play with finding a box with the right fit and getting the padding right. In an ideal world, your bike would never tip and your box would never touch the ground. But this isn't an ideal world. So the box needs to be ready for a fall or two, unless you don't really care about the battery, if that were the case, just wrap the battery in saran wrap and strap it to the rack.
I don't really know about the best padding setup. There are all kinds of foam options to choose from. Some might suggest forms of rubber or something like that as well. This is something I am working on myself, same concept and all that. There is a thread on this forum about home made battery boxes. http://endless-sphere.com/forums/viewtopic.php?f=3&t=12847 Plenty of inspiration there.
I don't really know about the best padding setup. There are all kinds of foam options to choose from. Some might suggest forms of rubber or something like that as well. This is something I am working on myself, same concept and all that. There is a thread on this forum about home made battery boxes. http://endless-sphere.com/forums/viewtopic.php?f=3&t=12847 Plenty of inspiration there.