How to charge the phone slower ? topic

In the times of high demand of ever more "fast charging " benchmarks I have a question. Fast charging is good and all, Especially on devices with replaceable battery! but for people like us who have Mate 7, fast charging technology is not really a desirable function. What I want is to be able to charge my phone slowly when I am at least, this is usually between 6-9 hours. We only have one battery on this one, so we really have to take good care of it. I know the battery time will become a huge problem in one year trust me..so I wonder.. how can I charge the battery as slow as possible ?
Should I buy a new adapter ? I also want something I can trust, that will not cause fire!