[Al Skierkiewicz]

Ryan,
This is not recommended practice. When batteries are used in parallel they need to be nearly identical in operation. (MK and Battery Institute experts agree that same age, same lot, same charge/discharge cycles must be maintained for parallel operation) Used FRC batteries have gone through enough charge/discharge cycles that they are as likely to self discharge each other as they are to increase amp hour capacity. Diodes can be used to prevent this and are available at RV stores.