Hi John!
I have a few Nanos and just got the Mini this week. I've played with rebuilding the OCC heads, but even if you start with dryburning and rewicking the OCCs, you'll be quite a bit ahead. Rebuilding the OCCs isn't terribly different (for me, anyway) than rebuilding the EVOD/Protank2 heads. I only got the Mini to see what the buzz about the RBA part was about.
Only reason I can see where you'd ruin the battery might be a poor build (ohmmeter should help avoid that). One tiny bit of difficulty I have is getting the leads trimmed well enough that they don't snag in the base.
The "better" option is what *you* like. I'd wicked up the RBA when I first got it (of course as I'm trying to get out the door to go to work) and I burnt the wick. Haven't taken the time to rewick yet, so I've been 3 days on the 1.2 OCC, and I'm stupid happy with it. I do want to get the RBA part done correctly to give that a whirl, but I can't stop refilling my tank!
I believe you're correct that the capacity is "smaller" with the RBA installed, but I still can't fill the tank above the chimney, so I'm putting in the same amount of juice regardless of using the OCCs or the RBA....
Cheers