Pin 2 and the IBBS
I would recommend not adding any other components to Pin 2, particularly an added series diodes as this reduces the input voltage presented on Pin 2. Since the function of pin 2 is to provide a trickle charge feature to the back-up battery so as to ensure that the battery can accept a full charge from the fast charge circuit which is enabled when main aircraft power is applied to pin 1 when the aircraft is operational, it's condition is best indicated by the behavior reported on Pin 5, "the info pin". When the aircraft is operating normally, pin 5 will report the internal battery voltage, when main aircraft power is lost, pin 5 is driven low to provide a warning signal. Therefore, the condition of the battery is shown by pin 5 during normal operation and really tells the story if there is an issue with the charging system. Under normal operating conditions you will see an internal battery voltage of about 12-15 volts, if you every see the battery voltage stuck around 10 volts or less, then the integrity of the pin 2 connection or capability of the battery (end of life) needs to be investigated.
Bob Newman
TCW Technologies, LLC.
RV-10 N541RV