You can use any Chargers rated at 5/12/ Maximum 30 volts adopter. Its just the higher the voltage the faster it charge... iPhone battery isn't affected no matter how Cheap your charger is that only cost 4$ however the sad fact is that; the Most damaging thing that will Harm iPhone battery is:
1. Playing Heavy Games such as Asphalt 8, PUBG, Mobile Legends, Garageband, editing Movies, 24/7 With almost no rest.
2. The second damaging thing is Using not so heavy games such as Subway Surfers, Piano Tiles, or any games that is less than 2GB of storage.
3. Using social media apps all day with no rest such as Youtube, Facebook, Instagram and etc.
4. The Next Damaging thing is if you always charge your iPhone While Playing Games.
5. Well this is common, Battery will be affected if you often Update for example iOS 12.0.1 then update to iOS 12.0.2 try skipping some iOS version to have less stress on battery.
6. The last damaging thing is jail break or download an app such as PPSSPP from a certain Fake Apps with some virus on it. Well, to make matters worse for example some of the storage like 2GB wont be recover even after you uninstall it unless you restore or reformat your Device.