*Source 12 x Second Hand ex Telstra 2 volt cells. 70 x 180 x 350. These will fit nicely.
These are a premium UPS battery with a design life of 15 years. They are AGM design apparently but are no where designated as "deep cycle". They have a maximum charge rate of .1C and , possibly more diagnostic , are able to be mounted either vertically or horizontally. This must mean that the electrolyte has a tenous role in the duty cycle. The batteries are available at 60 bucks for a 500 odd dollar list price battery apparently ex Telco, in the original packaging and with no witness marks on the terminals.
At first blush this suggests these batteries must be over provisioned and nursed in an Off Grid role.
The brutal question could be ; these batteries will last 15 years of doing nothing in a Godfather UPS role. However if you were to make them do something Off Grid wise and the battery was being pulled off the Manufacturer Spec Sheet (have not yet found and cycling vs life contention let alone specs). You might make inroads into the design life but the cost benefit puts them in front of purpose batteries such as the Century C105 type industrial deep cycle purchased Retail and new.
At very least this suggests some "hard stops". My first limit would be charge rate. Anecdotally I have heard of systems comprising this product just collapsing early in service. I can only conclude overcharging would be the failure mechanism.
My next guess is ; treated gently on depth of discharge. Clearly an Off Grid battery that cannot withstand any meaningfull depth of cycle is no battery at all.
Is it better to buy twice as many as you need and treat the aggregate more gently in an "Off the Reservation " role? Dont rightly know.
The charge controller is the epsolar tracer 4210A.