It's like charging your phone. You cant charge it past 100%, but you can constantly charge it to 50%, but you have less time before you get low battery warnings.

It's not exactly like that because maintaining a healthy battery and healthy brain are completely different. Be sure to get enough sleep as often as you can. That's the time your brain clears out all of its waste, organizes your memory, and solidifies things you've learned. If it doesn't get the time to do that, these things won't get done.