concern over battery banks

[halkading]

Greg,
My main AC power panel has two breakers to power inverters (only one inverter in my LX so one breaker doesn't do anything). Shut off the breaker and it kills the battery charger.

Question for you - do you have a odd looking round thing with cables hooked on each end near the marine style rotary switch (maybe a large diode)? One of the cables comes from the rotary switch and the aux battery contactor and the other side from the inverter. If it is a diode mine is shorted. I'm not at all sure what it is supposed to do. Any info will be appreciated.