Gary RV_Wizard
Site Team
There is no way to answer that without detailed and specific battery data. Neither the CCA rating nor the 20-hour AH or RC ratings are sufficient by themselves to evaluate. The problem is that battery power delivery is non-linear (Puckert's Law), so you can't extrapolate from one load to another. 40A for 30 seconds is a mere blip in terms of amp-hours, but still a substantial current draw that needs a lot of plate area. At a guess, that 200 CCA motorcycle battery you mentioned is probably in the ball park. They would typically be only about 12 AH, so not much staying power though. If I had a bit more room, I would opt for a small car battery instead, with maybe a 400-500 CCA rating and perhaps a 50-70 AH capability. Better to have and not need than to need and not have, right? We aren't talking much space or price difference.
One of the largest motorcycle batteries, e.g. for a Honda Gold Wing 1800, might give enough extra margin, though. I think they can be had with ratings in the 300 CCA & 18-20AH range. Here's an example:
http://www.batterymart.com/p-Big-Crank-ETX20L-Battery.html
