Delta 2 recommendations for daily use

Hi! In my country we only have like 4 - 5 hours of electricity daily, so I recently bought a Delta 2 to power up my laptop and router to work through the day, and maybe watch some TV at night. The most heavy load I'll do (and already did a few times) is occasionally connecting an 800W pressure cooker if I don't get to cook in time with the few hours of daily electricity. I've using it daily until it reach 20% and in the few hours I get of electricity I charge it to 100%, at 500W charging speed since I've reading that daily fast charge is bad for it. The question is, I'm doing it wrong? I've reading a lot of recommendations that I should charge it only to 80%, and just want to verify if that is true since it will means I don't get to watch TV at night lol, and also I don't know if I should slow down even more the charging speed. I will be using this thing every day for a long time because the electricity problems in my country won't likely be solved soon, and I need it to last at least a few years since where I live it is expensive af with the shipping costs and stuff so I won't be able to afford another one soon, so, what are the best tips to get the most of it while also keeping care of it?