It's a larger case then the standard VK, which is pictured next to it. It's a "works" unit, but it's not in a standard "works" case by any means, and if you notice, everything is mounted from the top, all the screws and screw holes are on the top, since the battery takes up the space on the bottom where I normally mount things.
I've been tempted to possibly fit the batteries down either side, rather than in the middle, so that I could mount things from the bottom as on a typical VK, but it's really hard to say whether that would be possible without actually doing it, for now, it's still a custom option, nothing really set in stone, so future units may have other improvements or changes, as needed.
The battery units will only be in the larger case for now. It's possible I could squeeze smaller batteries into a smaller case, but it's one of those to-be-determined sort of things, in this case, a customer was willing to send me a pack and let me play with it and take my good old time. For future units of this kind, I know what works now. For something smaller, with less battery capacity, still to be determined, it's possible, but it's about finding parts that will fit and do what I want.
As for removable/replaceable, good question! I used velcro, so it can actually be removed, but I soldered it in on this one. However, there's nothing saying I had to solder it in, I could have very well put some connectors on there instead, and you still could totally cut the wires and splice in some connectors. Then it would truly be removable, assuming you have a philips screwdriver. Although, I'm not entirely sure I really want customers poking around inside units, so I don't think I'll market it as a removable battery right now, but if you want a custom unit with connectors inside instead of it being hard-wired, no problem really, and the velcro is already there, so you're good.
For one that's a works unit like above, expect the works price, plus the cost of a battery and extra labor, probably another $20-30, but again, will depend on the options and battery used! I'm thinking around $80 to $90 depending on options. Prices will vary depending how cheaply I can get these batteries and the chargers.