to echo brian, I have had reactors that I had set to activate to fill a battery. I've used thermal expansion batteries in tandem before and I've used draconic evo ball of energy storage and a few others. Sometimes I can find the sweet spot where fuel put in is greater than fuel spent and energy produced is at or just above energy expended. In that case, I've just let it run. As it is now, I normally set it up to kick on at 30% of my battery and kick off at 90%. This lets me use a reactor that burns through fuel faster than I can produce it because the rf/t production is so high it fills up the battery in no time. The down time inbetween is where I get to build my surplus. I could never run it all the time.
It really depends on what your needs are and what you want. How complex or simple of a build do you want/need.
Currently in my world I have a 5x5x6 reactor with 8 cores. It produces 10k /t and uses 1.5 mb/t. I just let it run. It's not the most efficient design and certainly not the design I will stay with but it works for my needs atm. I also use about 5k/t so I just let it run. I get about 1k uranium surplus everyday. So I'm producing fuel faster than I am consuming it. I will setup gates and logic for it later but for the moment I'm perfectly fine with the setup.
Try different things. Here's a link to a video with some explanation for how it works (mechanic wise) that might help explain. Your idea might not sound too crazy with a large enough size reactor.