FACT 1. The breakaway switch is supposed to hold the brakes
for 15 minutes.
FACT 2. The 5 amp hour battery
will do that.
FACT 3. The smaller "house batteries" are about 74 amp hours. They'll hold the brakes
a lot longer.
FACT 4. When there is a house battery
then the breakaway system battery
is connected in parallel with the breakaway battery. This is necessary so the breakaway battery is charged with tow vehicle.
FACT 5. The current rating of batteries in parallel in the sum of the two.
I have a breakaway switch on my trailer. It's connected between the battery plus terminal, yes at the battery (house battery) and the break magnets. That's all that needed. The rest is sales hype.