I do the same. Trailer is hooked up to tractor cab with 12V wire plugging to front of trailer then to a battery on the trailer. 10A in-line circuit breaker at the trailer battery keeps the trailer battery from pulling too hard (overheat smaller wires) on the truck cable. The transfer pump starter, trailer LED lights, and chem pumps all pull off the trailer battery. Small charge circuit on the transfer pump also recharges trailer battery. I also have a common Square D type breaker box with AC breakers wired in to control some pumps & lights. The c.b.'s also serve as switches. I don't know if the 20A AC breaker is seeing the same amps in DC as in AC, but it works. If you short a wire, it will pop the breaker.

Also powers 3" electric hose reel.

Also, on this same DC system is a HD air compressor plumbed into a 100# upright LP tank. Compressor has 100# cut in, 120# cut out setting. We use this for blowing out the 3" fill hose. Have had this system for 10+ yrs. Works great also. No dependency on semi air. The compressor pulls of the same trailer battery.

Also, I have LED flashing lights mounted high on the trailer that are powered from the "switched" side of relays. They  flash while 12v pump motors are running. Did that to help prevent driving away from tender with 12V pump accidentally left on. You can see the strobes from a long-long way and say to  yourself....XXXX!! I forgot to shut the pump off.

We've had this setup now on 2 different drop deck trailers for about 15 yrs...maybe longer. Spraying & filling sprayer is normally a 1-man (me) job.