cell phone batteries life

Is it better to charge your cell phone every day or wait until the battery is almost dead?
My girlfriend and her mother thought to load the cell phone a day reduces the battery life. I think that was true in the older cell phone batteries, not more new, current. I prefer to make sure I have a fully charged phone every morning instead of the phone is dead when you need because you do not charge it daily. Who is right?
My mom and I are very similar phones. She takes it almost every day. I can upload mine maybe once a week, when reduced to 1 bar. So How thinkl working better?
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