If you only drive the car twice a month, you will need to also get a battery maintainer and plug the car into an AC outlet to keep the battery charged. The slight load on the battery even while the car is turned off can discharge the battery in as few as 5-7 days.
I have one, and don't have a maintaner. Then again, I drive my car at least 2-3 times per week. Brent Cobb has one with the battery maintainer. He once experienced a "dead" battery while at a shopping center, and had to push his car over to a bank and plug his car into an outlet there to get enough charge to start the car.
But - it's a HECK of a lot lighter than the OEM battery!
EDR