This morning I had one of those blinding flashes of the obvious. It is often stated, and I have done so myself, that the safe way to disconnect/connect a battery is to disconnect the negative terminal first and connect it last. The rationale for this is that without a ground reference the positive terminal will not arc through a wrench to ground if the wrench accidentally comes in contact with the vehicle sheet metal or frame.
This philosophy has its source in automotive mechanics where, if the engine is not running, the battery is the only potential source of current. This is not true in our trailers with multiple batteries, converters, and solar chargers which is referenced to ground at the distribution panel.
The positive terminal of the battery with its negative terminal disconnected is connected to the trailer’s 12 volt
distribution system which is still being fed by any other batteries, the converter if shore power is connected, and a solar system, if fitted, unless it’s disconnect switch is activated. While those sources are typically protected by fuses or circuit breakers, a short burst of high current is still possible.
I apologize for repeating this inappropriate safety guideline.