Interstate does not make batteries. They put their name on batteries made by Johnson Controls. Same as Walmart. So if you want a new deep-cycle battery, you can get the same at Walmart.
I have to leave my place where my fence is for sometimes over a week without checking on it. Electric fence runs on near nothing UNTIL some animal shorts part of it out, or a tree limb falls on it, etc. Then it uses much more power. It also make having solar handy if you are not there everyday to check it.
I have a 15 watt solar-panel, type 27 deep-cycle battery, and a controller. I was gone for three weeks last spring and when I came back the fence was shorted in two places. Still was working fine and battery charged.
Note - I would now use a controller on any solar panel. You can buy a new controller for $9. It used to be you could hook a solar-panel 15 watts or smaller to a full-size battery and not need a controller. Often not the case anymore. Solar-panels used to have built-in blocking-diodes to prevent the system from working backwards and draining the battery at night. Now - many do not have those diodes and assume the use of a controller. No big deal for $8-$9.