Open activity monitor and take a look at both the CPU and Memory tab and see what program is actually the problem. You can limit how much CPU usage a program uses at any given second, but that just means it's going to take more time to finish its task which will ruin your battery life if that task takes too long.
For my Mac Mini at home it's biggest problem is time machine. It creates local snapshots, then it does the bigger backups to my local NAS and when that happens CPU usage goes insane and the machine slows down to a halt. I switched from hourly backups to daily backups for that reason.
Also I wouldn't worry about 50% memory usage. That's nothing. Look at your memory pressure in activity monitor. If it's green then don't even think about it. It's not until it's yellow that you should maybe consider closing out of things, and when it's red you're probably going to start noticing the machine actually slowing down.