Best percentage to charge iphone?

My old battery broke cuz i charged it at 65
now i wait till it gets to 27-28 then charge it to 100

I charge mine to 100%

It doesn't matter when you charge it that much. What you don't want to do is charge it to 100% and leave it plugged in. The battery then throttles as its plugged in. Do that over a few years for several hours daily and you'll run up the battery cycle count.

You also don't want the battery to drain completely. Lithium-ion batteries can die permanently if they completely lose all charge.