What's the longest a car can sit without running before its' battery needs a jump?

[severous01]

just go buy one of those little solar panels and put it on the dash, wire it into the cig lighter or put a cig adapter on the end...

at 2 amps all day it dont matter how long it sits there, it'll always be charged.

to answer your question, you'll be doing more harm that good by just starting it up and letting it run for 10 min. it takes more than 10 min to recover from starting the car and start actually charging the battery above use from starter.

there are several voltage maintainers and small chargers for home/garage use at walmart or autozone.