Using an extension cord for a level 2 charger

<$10/yr, so a $400 EVSE would take more than 40 years.

We drove about 10K/yr in our Fit EV, our electricity was between $20 and $25 per month.
If the the L2 was 3% more efficient (generous), you'd save ~$0.75/mo

 

You’ll be long dead before the meager savings of a slightly more efficient Level 2 EVSE pays back its initial cost without even factoring in any installation costs. You buy one for convenience, not economy.
Edited to include @insightman ’s sage observation that it also allows robust preconditioning which is worth the price right there!

However, for those with TOU rates it could be more economical if it keeps your charging in a lower rate period. If you drive enough EV miles and the $/kW offset is high enough, you could factor in how much 2 vs 12 hour charging Is saving you. It would also depend on how long the lower rate period is. It would have to be shorter than 12 hours for the Level 2 EVSE to realize any savings for you.

For me, I wanted to be sure I could keep my Clarity fully charged even if I took multiple local trips in one day or forgot to charge. Turns out I’m seldom charging more than once a day, but I absolutely appreciate the convenience and the ability to track my kWs and compute how much I’m saving.

 

I guess a L2 charger is more for convenience as @KentuckyKen says.

I am fortunate to have the car plugged in overnight on a L1 OEM charger because it sits there for 16 hours during the work week and not have to pay a cent in petrol.

Also having access to other ICE cars makes it possible to do this...

 

I charge at home using 110v on the weekend if my EV range falls really low, but at work they have plenty of L2 14-50 ports so I bought a $170 L2 Duosida charger just to be able to charge at work, charges to full in about 4 hours. The benefit is the reduced time. If I charge at work using the level 1 when my EV range is below 10 miles, I won't even get a full charge when I get off work (about 9 hours)

Haven't really saw benefit of expensive 32A charger as personally I really don't need that fast of charging speed

 

Convenience AND robust preconditioning (which I guess is a form of convenience).

 

just make sure the extension cord is made out of higher gauge wires (6 or 4). otherwise, you are running the risk of electric fire because amperage fluctuates during charge cycle. all in all, it's not a good idea but if it's not a permanent setup you may be o.k.

 

If you have normal length in wall run to the outlet you only need a 12 gauge extension cord up to 50 feet. No need to go to 10 gauge let alone 6 or 4 for the OEM Level 1 EVSE. It is advisable to use the shortest one possible and follow all mfg recommendations and local codes.
For the 16 Amp Level 2, I could see going up to a 10 gauge, but not larger than that and even then, a 12 gauge would be fine for 25 ft.
At the risk of losing my man card, I will say “read the instructions” on the extension cord. It will have the Amperages listed and the distance limitations. Safety first.

 

I found the OEM Level 1 cord length to be too short to reach the closest 110v plug in my garage. I use a 25ft 10gauge extension cord, which seems to do the job without any hot spots in the cord:

https://www.amazon.com/gp/product/B01F6E1DIW/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

I've connected at KillaWatt device on the outlet and noted it doesn't draw but about 10-11 amps while charging.

 

I have 240V outlets in the garages of both my homes, installed for a Tesla I used to have. I wouldn't have gone to that expense for charging a PHEV, but they're really nice to have. I bought a 30 amp EVSE for my Clarity.

I have a deposit down on an Audi Etron, arriving (they say) sometime before the summer, so I'll be needing the full power again soon. Audi says they have partnered with Amazon to do 240V 50 amp installations; details to follow. If Amazon is getting into that business, we may see substantially lower costs in the future.