Hi
Regardless of what else you do, you need some sort of
12V battery on the trailer to run the breakaway setup. Normal current drain and run time get you into something over about 40AH for that battery.
Proper care and feeding is important for any battery, regardless of what type it is. That's just the way it works. With reasonable attention, a lead acid battery will be > 80% capacity after 5 years of use. On a 1988 trailer, even at a 5 year life, yes that's a lot of batteries over the years. Hopefully you also bought tires and brakes a few times over that period as we'll
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On a modern trailer, the "charge wire" on the 7 pin connector goes directly to the battery through a fuse or breaker. All the "stuff" in the trailer then is switched to battery (or not) depending on how you want to roll. You can read a lot of threads here on the forum about how much or how little good that seems to do ....
Bob