Can You Use an Extension Cord with an EV Charger (EVSE)

Extension Cord Guide

The simple answer is YES but you have to follow guidelines and check for heating
The problem with using extension cords with EV Charger is that they can overheat and melt if the wire is too skinny). Then bad things happen, Solution use the proper wire gauge (AWG) and check for heating after charging for 1 hour.  

Warm is Ok, Hot like Coffee is not. 

SUGGESTION - Avoid lighted extension cords. They have very poor plug/receptacles

Here is the Guide - EV Charger vs Extension Cord Length

EV Charger		25'	50'	100'
12 Amps		AWG 16	AWG 14	AWG 12
16 Amps		AWG 14	AWG 12	AWG 10
25 Amps		AWG 12	AWG 10
32 Amps		AWG 10

How Much Current can my J1772 Cable Handle?

Generally the pins in the J1772 handle are all the same - 16A to 50A.  It is the wire size (AWG gauge) that makes a difference
Here is a table for a 25' long EV Charging (EVSE) Cord. You will notice that the power loss is very small when compared to the power delivered.  You do have to check the temperature of the cord and connectors after charging for 1 hour.  Warm is Ok, Hot like Coffee is not. 
Table - J1772 Max Load vs Cord AWG

Cord	Max Amps	Volts	Watts	Loss (W)
AWG 18	12A	120	1,440	46
AWG 16	16A	240	3,840	51
AWG 14	25A	240	6,000	78
AWG 12	32A	240	7,680	82
AWG 10	40A	240	9,600	80
AWG 8	50A	240	12,000	80