If all you want it a means of operating slides from an auxiliary battery, then you can use just about ANY 2 volt battery for the purpose. It will be LIGHTLY tested when used for that purpose. If you end up using it for MORE things while dry camping (cool weather running the furnace) then you'll need a better battery so it can withstand frequent discharge/charge cycles. In THAT case you'd be better off just installing a second battery (best results would be to install two batteries of the same size, capacity and age at the same time) but just getting a similar battery to your current one would still be a help. For dry camping without utilities OFTEN you really need a couple of true "deep cycle" batteries (not a modified starting battery like the RV/Marine deep cycle). Starting batteries do NOT stand up well to deep discharges and usually will give up after just a few.
Good luck / Skip