Copyright 2019 Discovery Owner's Association, Inc.

Battery Charging

The purpose of this page is explain how the D's coach and chassis batteries are charged, and also offer some tips if your coach batteries are not charging. This pertains to all D's at least 1998 forward. It is possible that this information may not apply to some 1997 D's.

Almost every Class A motorhome has a seperate battery for the coach and a seperate battery for the chassis. The coach battery provides 12 volt DC power to the "residential" functions of the motorhome - interior lighting, refrigerator, furnace, inverter (if so equipped), etc. The chassis battery provides 12 volt DC power to the engine, transmission, headlight, turn signals, etc. It is very important that these batteries be isolated from each other so that, when not connected to shore power, the coach 12 volt DC requirements do not draw down the engine battery, stranding you as you would not be able to start the engine. Some manufacturers provide a simple isolation diode to seperate the batteries. However, a diode has a voltage drop across it, and the result is that the battery will not be fully charged. Since the mid-80's, Fleetwood has employed a more advanced methodology of isolating the batteries with a relay device that allows the coach batteries to fully charge. The latest device that Fleetwood uses is made my Intellitec and is called a Bi-Directional Isolator Relay Delay. Some people call this "BIRD" for short.

Intelletic BIRD

The really neat thing about this device is that BOTH your chassis and your coach batteries are charged by the alternator when you are driving. When you are stopped, BOTH engine and chassis batteries are charged from the inverter/charger. If neither coach or chassis battery is being charged, the batteries are fully isolated. The BIRD also senses heavy loads on either battery to prevent the wrong battery from being inadvertently discharged.
The unit operates by sensing the voltages on the coach and chassis batteries. When either of these voltages exceeds 13.3 volts for approx 12 seconds, which happens when either battery is being charged, the control will close the isolator solenoid, which will connect the batteries together and charing them both. Note that this charging current can come from either the inverter OR the engine alternator. If everything is working properly, both your chassis and coach batteries are charged while you drive and also when you are plugged in to shore power.
After the solenoid has been closed, the BIRD continues to monitor the battery voltage. If the ignition switch is off and the battery voltage drops below 12.8 volts for approx 5 seconds, the solenoid is opened to prevent the chassis battery from being discharged by the coach loads. This may happen if the inverter/converter is heavily loaded or if shore power is unplugged or interrupted. When the voltage goes above 13.4 volts again for approx 5 seconds, the solenoid closes again to supply charging current to both chassis and coach batteries.
If the ignition switch is ON, the control allows the voltage to drop below 12 volts for approx 5 seconds before the solenoid is operated to insure the alternator's full output is available to the chassis battery for charging and/or maintaining chassis requirements. When the voltage goes above 13.3 volts for approx 5 seconds, the solenoid will close.

The BIRD requres a source of 12 volt DC power to operate. In the D, this power is taken from Fuse F22 in the Battery Control Box in back of the inverter in my 1998 D. If your coach batteries are not being charged by the alternator when you drive, check this fuse. If this fuse is blown, your alternator is only connected to your engine batteries.

Well, let's hope that your inverter/charger didn't fail! Try the following before you panic!
Check the push-button circuit breakers on your inverter. You should hear an audible click (which is the internal transfer relay in the inverter) when you apply shore power and you should also hear a slight hum and the inverter cooling fan may come one. On the 1000 watt inverter, the motherboard mates with a connector near the face of the inverter. Heart advises that sometimes this may jar loose a bit and suggest gently hitting the front faceplate of the inverter.
The inverter is connected to the monitor panel with an RJ-15 telephone jack and cord. Sometimes, the plug does not make a good connection with the jack on the inverter since it is in a harsh environment with a lot of dust. Unplug the connector and carefully wipe the contacts with a pencil eraser - CAUTION! - make sure that you get it plugged into the proper jack!
The BIRD is a highly reliable device, and any problems associated with it are usually either the failure of Fuse F22 or a bad ground connection to the BIRD unit. Fleetwood did a good job of hiding the BIRD - I think it may be behind the battery control box in back of the inverter.


The DISCOVERY OWNERS ASSOCIATION, INC, was formed to promote the sharing of information and the camaraderie of fellow Discovery motorhome owners. Membership in the club is limited to owners of Fleetwood Discovery motorhomes.


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