Don't do it! Your "bad" battery will suck the life out of the good one, shortening your run time AND the life of the good battery. Hooking up a couple that are different amperage doesn't cause a problem as long as both hold a good charge, however, you'll lose the lower amperage battery first and then it'll begin to draw down the other one, which negates the benefit of having the higher amperage battery. Best bet is "marry" up your batteries to get the best results, making sure to keep them charged at all times. A discharged battery begins to deteriorate very quickly and will be damaged in a relatively short time if left that way. If you're storing for the winter, check the charge a couple of times to make sure you haven't lost any charge and you'll be good to go as soon as the weather turns in the spring.

"God made men, Colt made men equal, Winchester made men equal at greater distance."