How long will it hold a charge for?

1-2% discharge rate per month.

For reference... a traditional lead acid battery will discharge at a rate of 4-6% per month.

Therefore you can pull the unit out of your vehicle in 1 year and approx have 80-90% charge remaining.

Enough charge to jumpstart in an emergency situation. We always recommend keeping your RUGGED GEEK jump starter 100% charged in case of an emergency.