: good reply but I'm afraid I'm only one of few people in this forum section who understood what you meant
Not everybody has EE or electronic hobby background
Here is my take on this. Your battery is 3.7-3.8V, and once you plugin that 5.2V charger into micro-usb (5V standard) interface of your phone conector it depends on tolerance of its input of the internal converter chip (5V -> 3.7V for charging). This can't be guaranteed and will vary between phones, just my guess. Considering your have 500mA charger, I can also guess you don't have the latest brand name smartphone where most of them use 1A-2A chargers. Another thing, everybody makes 5V micro-usb wall chargers, and the fact that you have one rated at 5.2V sounds like some cheap ebay part? So taking all this into consideration, I would probably stay away from that charger. Look up on Amazon, you can find a nice one under $10, like from Anker or Ravpower.