I enchanted a sword with a double effect and was annoyed at how quickly it depleted so I used a console command (player.setav rightitemcharge) with a high number. I forget what it was but I didn't notice much of a change so I guess there is a max charge level?

If so, what is it?

The maximum charge is the capacity of soul used. How much of it is used per attack depends on skill level and the enchantements themselves. Using two enchtantements will deplete the charge quicker. However boosting skill will decrease the charge cost.

http://www.uesp.net/wiki/Skyrim:Enchanting_Effects#Weapons