Third battery plus solar panel?

[popotla]

I have a 100-Ah lead-acid starter battery linked in parallel (via simple on/off cutoff switch) to another lead-acid starter battery (110 Ah) which I use for fridge etc. I’m going to be obliged to use a piece of equipment, run most nights, which requires at least 30-35 amp-hours, so the 110 Ah starter battery, to be subjected to constant discharge-charge, isn’t going to do the job for long.

My idea is to use a third battery, a lead-acid deep-cycle of about the same capacity as the existing two, and connect it in parallel, using another on/off switch between it and the existing second battery. Thus I can continue to isolate the main (first) battery when the engine isn’t running and, if I wish, isolate the new, deep-cycle from the existing auxilary. I’ve done the maths bit and to supply extra charge and to fit with the way we expect to be using the vehicle, plan to use a 100-W solar panel (the highest capacity I have roof-space for) and link this via a regulator and meter to the new deep-cycle. Ideally, the solar panel could be switched between the existing lead-acid auxiliary and the new, third battery, the deep cycle?

Will this work?

[Pedro_The_Swift]

why not an AGM storage batt?
and with my limited knowledge, you must replace the 35amps within the next day so at a max 5-6amps per hour it will take a whole good sunny day to replace via just the panel. any car charging done would
be a bonus.

theres gunna be a lot of switching going on

[popotla]

"why not an AGM storage batt?"

Because an AGM battery shouldn't be run in parallel with a lead acid battery. These are batteries of two different types and so shouldn't be mixed. if I am wrong in saying this, will someone please tell me.

"you must replace the 35amps within the next day so at a max 5-6amps per hour it will take a whole good sunny day to replace via just the panel. any car charging done would be a bonus."

Absolutely. The solar panel charging I regard as "help", not sufficient, alone, to replace the 30-35 amps (which is not, in any case, the ONLY consumption). I also have a 40-litre Engel fridge.