Battery Level Indicator
The LED is a highly visible and intuitive indicator of your battery's strength.
With a standard charge on the battery, it illuminates for about 3 seconds when the guitar cable is first plugged into the Bass jack; the circuit powers up and measures the guitar's battery voltage, then sends a pulsed intensity pattern to the LED which indicates the battery voltage.
If the battery voltage is too low the LED flashes quickly on and off for 5 seconds. You will want to change your battery before your next playing session. If this is the first time you got the warning and you have been playing the instrument on a regular basis, there is no need for concern - you have enough power to play out your gig (for more information on batteries see FAQs).
If the battery voltage is more then about 7.0 volts the LED will flash in a 3 step sequence. The first step is at maximum brightness. The 2nd step is at a reduced intensity starting at 9.2 volts. The intensity is modulated in semi-log fashion to accommodate the ability of the eye to recognize changes in intensity. The 3rd flash is back to full brightness. In the picture 3ZB installation below, the LED is bright enough to scale back the camera's light meter.
If the battery voltage is more than 9.2 volts then the pattern would appear to be one 3 second flash. This would mean you have either a new 9 volt battery or are running an 18 volt (two batteries) setup.
With the 3ZB 18 volt option, you can either choose to change your battery at the first sign of dimming. This would be appropriate if you are using the 18 volt system because you want lots of head room. Or you can wait for the fast flash sequence described above. This would be appropriate if you are using the 18 volt system because you wanted very long battery life. Either way you will get increased life from an 18 volt system (more info from FAQs).
Since this feature is unique, you'll have to decide where to mount the LED. The LED is small, 3 mm in diameter, and can be press fit into a mounting hole. Common locations are in the top of control plates (like those used on the Fender Jazz Bass or the G&L) and in the back through the control covers. The link will open a new window where you can see a couple LED installations.