I only get about 4 weeks out of a charged battery. When I say new , I don't mean a new battery every month . But I have 2 battery fencers both 12v . Other is a Cheta. I buy a new battery most years . Also ; they are actually 663 s. I sometimes swap one out of a tractor to the fencer and vice versa. It's hard on a battery , if you let them discharge completely , before recharging. As is leaving them dead for long periods , or leaving them directly on the ground. I use a mineralbucket lid under them . There are lights on the PEL fencer , that show you it's output/state of charge , so that you can change the battery as it slows down before dying.
I bought a solar panel in Aldi last year . A waste of money imo. Doesent prolong times between charges.