My charging speed too much slow

You need to check the list:

• The cable
• The AC input
• The connecter on the phone
• the motherboard

@sijanmahmud use an ammeter and connect it between your charger and your phone. See how many amps your phone is pulling. this could be an issue with your charging port, charging board the PMIC or even just the battery. Check your charging port for any bend or corroded pins. Clean the port with a few drops of high grade isopropyl alcohol and a few puffs of compressed air.

If none of that works, It may just be time to open the phone and to check out the charging board. A new battery is always advised to rule that out as the main cause.

Since iFixit does not yet have a specific guide for this phone, use something like this video to work on your phone.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!