Please consider offering battery boxes that are sized such that your batteries fit snugly within them. For example, I am unable to locate any available battery boxes that are appropriate for your 12 volt 100 AH 'mini', and I suspect that this is also true for most of the other batteries in your range.
What's your situation? Batt boxes are usually used in mobile applications and the most important part of mobile installation is securing the batt(s) reliably in position to solid structure. This requires securing the batt itself; the case plays no part, cannot be relied on, to safely mount a batt. Sometimes I use common cheap plastic batt cases for cars, rv's - the case is always somewhat larger than the batt and I drill the bottom of the case to accomodate the brackets or rods needed to secure the batt tightly to solid structure. In this type of install, the case is essentially just a dust cover, reducing UV and direct rain and spray on a batt. Holes in the bottom of the case drain any water. The batt secured to structure holds the bottom of the case in place; the top can attached to the case w/webbing or some other reliable system.
I have determined that the Mini battery line fits perfectly into a Camco Dual Battery Box #55374, which in turn fits perfectly into a standard 8" trailer tongue battery rail. This despite the pubished dimensions indicating that it will not work.
It works because both the battery and the box are tapered -- they get smaller towards the bottom. The interior dimensions published for the battery box are at the bottom, while the exterior dimensions published for the battery are at the top. But the bottom of the battery is much smaller, and the top of the box is much bigger, so everything fits perfectly.
I installed this combination on my tongue today and it's like they were made for each other. The width and height are comfortable, NOT tight -- there is much extra room in the length dimension to install shunts, shutoffs, or anything else you plan.
Note that the expensive (and secure) metal boxes are NOT tapered, so none of them work well. If someone offered a tapered security box, I would be interested in upgrading (I found the Camco box for only $32, not a huge investment to abandon).
Wattcycle asked me to share a few photos of the fit of this battery and box as installed on 8 rails.
The box also has plenty of headroom, despite the battery sitting on a 5/8" wood retention cradle.
