These batteries tend to cost alot for the amount of power and forget any warranties. You can save by buying them at places like the home Depot though. The car battery is a lot larger and needs to be kept in a portable plastic battery container because it must vent Hydorgen gas and invariably some H2SO4 (Sulphuric Acid). Even the so called sealed car batteries seem to leak acid.

The advantage of the car battery is the extra life and that it can be readily charged in the field or coming and going, from the vehicles alternator.

Some guys just mount a second battery in thier vehicle and have an isolation circuit that charges the aux. battery but will not discharge from the main.

How about it? anybody got a circuit diagram?

Have Fun,
-Rick