Juniper Systems Allegro CE Manual - Manual (Page 39)

Hardware Features Page 2-27
Battery Gauging Explained
The Allegro's intelligent battery gauging circuit helps you efficiently
maintain the batteries for applications. The percentage of remaining
charge in the batteries is indicated through the battery status system
tray icons. The gauging works for both NiMH rechargeable batteries
and alkaline batteries, although the mechanism is different, as
outlined in this section.
❖ Note: Battery gauging is provided as a tool to help you manage the
batteries. It does not affect the performance of the Allegro or the batteries in
any way. If the gauging circuitry is not properly synchronized with a
NiMH battery, it may show erroneous readings. Please read this section on
battery gauging so you understand the proper setup, functionality, and
limitations of battery gauging.
How Battery Gauging Works for the NiMH Rechargeable Battery
The Allegro employs a circuit that watches how much charge is
added to or removed from the rechargeable battery.
To illustrate how this circuit works, imagine the battery as a tank of
water. The battery capacity is like the size of the tank in volume.
Watching the charge is like watching how much volume of water
flow into or out of the tank.
Gauging the battery is like gauging how full the tank is, without
being able to see into it. You must know the size of the tank and how
full it was to start with to determine the amount of water in the tank.
As water flows out of the tank, the percent full can be calculated by
subtracting how much water has flowed out of the tank from the
starting point and then dividing by the capacity of the tank. This is
exactly what the Allegro does, except it monitors milliamp-hours of
electric charge instead of the volume of water.
For the battery gauging to work correctly on the Allegro, the following
values must be known about the NiMH battery pack:
- Charge percent
- Capacity
Setting the battery charge percent and capacity are both discribed
earlier in this chapter in the Setting Battery Charge section.