Our team uses 5-6 batteries changed out after EVERY match. We want our robot to have top performance during every match. We usually have a lot of motors and an air compressor that runs a lot of the match, so our battery is pretty low by the end of the match.
Also we buy all new batteries every year. Batteries from the one year previous are used for practice in the shop and programming and testing the bot in the pit.
Now to the question that you originally asked, I think that you could extend the matches a bit, but no more than 1 or 2 minutes.
Honestly from a field coach position, the matches are very fast, and done before you know it. Also I am not sure that I could take the stress for another minute or two.
