Found myself on a Porsche forum reading about lithium automotive batteries. Spent some time reading comments about the Antigravity brand battery, they had a rep posting and answering questions. Seemed fairly safe and had a cool Re-Start feature. You get a little remote with the battery. When a low voltage limit is reached the battery shuts down to prevent further discharge. When you arrive at your car and it is dead, you press the remote and the battery wakes up and provides enough power to start the car. No need to access the trunk. Then I saw how much it cost.