I purchased 3w LED replacement bulbs for my porch lights. Cheap bulb, color matches normal bulbs, more lumens and saves tons of energy.
I'd like the details on your porch LED product choice. We too use LED lighting in our house. But the cheapest I've found them was at Costco 3-pack of 5W LED "Lights of America", (Made in China) for $15.00 on sale. The metered power usage is actually 4W and the quality is not so good. Out of (6) we bought during six months we have had two go bad. Light output is great for inside. We use LED strips in our back yard, two strips @ 15w each so 30W total. It illuminates a large space and we are happy with it. My said solar setup was more of an academic experiment and not something that is setup full time.
Efficiency is always relevant, as well as wear and tear. Its not really saving money if the savings = replacement cost. Then its just a waste of time.
Increase of power rates, will probably also have the same proportional relationship to the cost of goods everywhere.
Honestly, there is little difference if any at all, if the AUX battery is doing duty in a truck powering a fridge or in my case powering 12v lights. When we travel and camp, my Aux battery pack gets loaded into the truck and does duty in camp as a portable power pack.
For the OP, if he parked in the driveway he could illuminate his driveway via 12v light in lieu of a front yard light... That would save a little $$