Lowest I'll every let it drop is 35% and a max charge of 75%-80% that's usually the best state to keep a lithium ion battery. Full charge of lithium ion cells leads to the cells decaying quicker, too little charge often leads to them dying off. Keeping enough energy to evenly distribute among cells tends to give them more life.
Though I don't use a Samsung device, I typically plug in my phone when it's around 20-45%. Sometimes when I get home, for example, and it is within that range, I may just give it a touch-up to 50-70% and then let it be until I charge it at my bedside.