Originally Posted by JimmyZ
What's "the Bird unit"?
Should actually be spelled B.I.R.D. (also referred to BIM system)
The Bi‐directional Isolator Relay Delay or B.I.R.D.® is a core piece of DC Managment Systems that
includes both a coach and a chassis battery. Its has 3 primary functions
1) Bridging two battery banks together when a charging source is present from either one.
2) Isolating the batteries when the charging source is removed or when both battery banks are
3) Providing aux start power when the chassis battery is low and unable to start the vehicle.
Every coach has a different wiring approach. Usually somewhere under the "hood" you will find large cables going between the coach and chassis batteries. In between all of this you will usually find a large 100 Amp circuit breaker and another battery charge monitoring device BIM. Mine looks like this
My understanding of its function is it allows either the chassis alternator to charge the coach battery or the coach battery charger to charge the engine battery which every way is appropriate.
Hope that helps. Im sure others will respond and perhaps explain it better.