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Depends on what your trying to run and for how long. Most new SLA batteries have no trouble holding a charge above 13.5v, but you want to avoid discharging them below about 12.6v for preservation. Put a battery voltmetre on it and watch it as its being used, stop it when it gets down to 12.6v - that is the useful time you will get. Going deeper, like right down to 12v will significantly shorten battery life, even deep cycle ones.
A 18ah and 7ah are not big, and I certainly would not be running heat straps off them. You could easily run a Dob push to system, like the Nexus, but for EQ mounts I would want much more AMP hours. I have a 40ah SLA that I use, with a voltmetre, just for my heater system in the field. Add up the draw of each of the things you want to run and come back.
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