[supergeek]

The main limit is minimum transaction fees. A gas station is usually at least a $20 transaction. Since most level 2 charges are about $1 of electricity per hour, you're paying massive credit card fees for short charges. The apps all support some sort of balance to combine charges into large single transactions.

[maxerickson]

Soda machines that take cards are common. It doesn't seem like small charges are a real problem.

So much the better to pay less fees, but I can't imagine it is really driving anything.