TwoSix
Everyone's literal second-favorite poster
Possible tweaks:Well like I said, it's still a work in progress. I haven't quite figured out how to deal with the "everything resets to 100% after every battle" aspect of it, but it certainly does need to be dealt with. (Or not, depending on how you want the game to run. I'd prefer some kind of lasting attrition.)
1) Roll at the end of the turn when you cast a spell. If that spell slot doesn't recharge on that turn, it's burned out until the end of a long rest. (Or short rest? Spend a different class feature to recharge slots? Maybe spend Hit Die for a more "physically channeling the spell" feel? Lots of ways to play it.)
2) Start with a d4, scaling to a d6 and a d8 as the caster level increased.
3) Make it so you have to roll over the spell slot level, not just on. That way even 1st level spells have a small fail chance.