This would be nearly impossible because micro-usb and usb type-c use different pinout (different number of pins...) and require different layout of the connection points on the charging PCB. And also the size of the usb-c socket is different.⏎
To do such modification it would require altering the charging PCB board, speaker housing (hole for the charging socket) and jumping (soldering very thin enamelled wires) from the usb-c connector to the different points on the charging PCB board.

Also this wouldn't increase the maximum charging speed, it would just be for the convenience of using one type-c cable with different modern devices.

You can purchase charging sockets from ebay by searching for "jbl charge 4 usb-c port" (without the quotation marks) or if you don't feel like replacing the charging port yourself, there are mail-in repair services available also.

You can buy ports from ebay by searching for "jbl charge 4 usb-c port" (without the quotation marks) or if you don't feel like replacing the charging socket yourself, there are mail-in repair services available also.

If the keyboard doesn’t work with the new batteries, doesn’t charge the batteries, or doesn’t communicate with the unifying receiver, a mainboard replacement may be necessary. The replacement circuit board can be purchased via eBay. Search eBay for “210-000797” which is the code for the PCB.

Hi,

the pinout for the micro-usb socket, looking from the top side (3.5mm audio socket is on my left and USB port is on my right):

1. Most left line, line #1 on the micro-usb connector is GND. Goes to the pin #5 (also connected to #6 and #7) of the large 11pin connector labeled J602.

2. Line #2 on the micro-usb connector is ID which is connected to the GND - pin #5 (also connected to #6 and #7) of the large 11pin connector labeled J602.

3. Line #3 on the micro-usb connector is DATA +, which goes to pin #4 of the large 11pin connector labeled J602.

4. Line #4 on the micro-usb connector is DATA -, which goes to pin #3 of the large 11pin connector labeled J602.

5. Line #5 (most right) on the micro-usb connector is VCC/+5V, which goes to pin #1 (also connected to #2) of the large 11pin connector labeled J602.

Hi,

for anyone interested - we are offering the micro-usb socket replacement service for JBL Charge 3.

You can google “getgui charge 3 micro-usb” since its probably against the policy to post links here.

Simon