actaully the opposite is true - the right type of charger will lengthen the life of a batt by a wide margin if hooked to your batts all the time you are not using it. A 3 stage smartchger type does not "trickle".. it floats so the batts always stay 100% charged...and that's what makes 'em last. Read more here about batt types and charging here:
good reads about agm's
Deep Cycle Battery FAQ
http://www.vonwentzel.net/Batt....html