For an english guide I’d recommend RachtaZ (https://youtu.be/ZfjK6GiF-L8) the guide is a little outdated i.e. the tutorial of the game has been updated since then but most if not all the information you’ll be given in the guide will still be relevant. If you happen to speak german Siegismund has an entire tutorial series that goes into a lot of depth and is honestly one of the best tutorial series I have ever seen for a game. If you decide to start playing I’d also second the suggestion to not play solo and either find a friend to learn the game with or someone who is already experienced. Also some people might recommend playing the secondary solo gamemode called quickplay/soul survivor (the name is being changed to soul survivor in the upcoming update) but it’s a lot quicker paced and lacks skill based match making so you’ll have to deal with even more very experienced and highly skilled veteran players.
Probably voiding warranty for any phone that has its battery replaced by the user instead of having it done at an apple store/apple vertified store. Or some good old planned obsolescence where the phone detects a replacement battery and just stops working as fast as it used to. Anything to get people to buy the next new iphone every year.