Trailer brake pad life

Actually brakes pads/shoes/hubs should be looked at much more often than a battery. I pull the hubs each spring and see whats going on.

How long brake pads on any vehicle will last is very subjective but I replace my 5th wheel RV/GN flatdeck trailers/car hauler/tri axle stock trailer brake shoes at around 40k-50k mile range all depending on how they look. And I don't just mean if their worn. Brake shoes and pads can have other issues also and need to be replaced.

I also find the magnets are pretty well shot after 3 yrs/15000 miles while the brakes were still at 75%,this is towing with a exhaust brake.

i take my trailer in every year to have the bearing packed and the braking system checked. just do this every year and you'll do fine.

I hand pack my bearings every year and check them at that time. I usually change them about every 3-4 years. I put on 6-10K miles per year. So I'm guessing about every 30K miles they are to the point I change them. But I've had magnets go bad much earlier than that. When it's time to change, I just replace the whole assembly, including backing plate.