For the application I would suggest Lithium as they are lighter in weight and have some amazing "Features" Two companies who's products you should Check out are Battle Born and Bioenno power (Link on last below)
DO check with the company to insure they are what you want.
An aquantance of mine who does a podcast (Gordon West/Ham Nation) brags on Bioenno power... Claims they hold their output voltage fairly constant till they are all but dead. This is important for your use. also though I can not state for a fact I think you can run 'em rather far down (more so than a Lead Acid) so 50 amp hour of LI would be better than 75AH of Lead Acid (About a group 24)
bioennopower.com/
