Volvo VNL Operator's Manual page 306

Electrical System 301
Battery Protection System (option)
An electronic battery monitor ("Battery
Lifeguard") may be installed in the electri-
cal center. This monitor will disconnect
certain circuits if it senses that the battery
voltage falls under a safe charging level.
Before disconnecting, the monitor will
sound a loud and distinct alarm, alternating
long and short beeps, for approximately
60 seconds.
At the end of the alarm, the monitor discon-
nects circuits to protect the batteries. When
the batteries are charged, either through the
vehicle alternator or a connected battery
charger, the monitor will automatically re-
store power to the disconnected circuits.
Disconnected circuits are connected to fuse
positions F15 through 35. These circuits are
W3002365
primarily feeding the sleeper area and
headlights.
Unless the batteries are held at an elevated
voltage for several hours, they will only de-
velop a "surface" charge. That charge will
quickly go away and the relay will retrip.