Function; An Example - Progress Direct Systems Volt Tattler 2 Owner's Manual

Function

Volt Tattler 2's thresholds are fully programmable with a variable DC supply and a high impedance volt
meter of sufficient precision and accuracy. This means that you can adjust Volt Tattler to accommodate
your anticipated operating conditions.
Volt Tattler 2 can provide practical protection for any piece of equipment powered by DC voltage from 4
volts up to around 28 volts. It draws less than 1 milliamp
practical even for Portable and QRP operation.

An Example

Suppose that you are a ham radio operator running a QRP station for Field Day. You understand
that your batteries are going to deplete over the day. You can set the high voltage level to, for
example, 15 volts and the low level to 10 volts (or check you manual for high and low limits
under which your rig will operate properly). This way you are warned against high voltage levels
while adjusting things during setup and then you can be warned again later when your available
voltage drops below a level that allows proper operation of your equipment. This can be
particularly useful when transmitting on a weakening battery.
1 Near 13.8V
1 of current in normal operating mode making it