ECones
tenbear means for you to measure the engine battery while it is running - its alternator should be hi 13 to 14+V, depending on engine battery charge state.
i am suspecting something in house is drawing a lot (maybe a short), or else the BIdirectional Relay Delay unit that controls when to charge both batteries at once. this BIRD turns a solenoid (switch) on or off depending on the charge state of either and/or both the house and the engine batts (this is what your quote was discussing).
the cheap $30 solenoid that BIRD controls notoriously can get stuck and cause all sorts of strange things