I use reconditioned RV batteries that I am able to get locally. 6v-110Ah. Run in banks for 12/24 volt operation. Don't overlook Surplus handcrank gens for mil. radio. More modern versions are usually 12/24v. Pain in the A** to use but is always there for como. Even the older versions like the kind I use for WW2 gear are usefull for charging usung the 24/28v supply for the filements for light battery charging.
Lowe's sells a small solar battery charge maintainer kit for around $50 that is good for gel cells.