EXFO FTB-500 - Manual (Page 275)

Maintenance
FTB-500 267
Recharging the Batteries
Recharging the Batteries
Your unit uses smart lithium-ion (Li-Ion) batteries. The number of batteries
that power your unit and that come with it depends on the model that you
have purchased. There are two batteries for the four-slot model, and three
batteries for the eight-slot model.

The charge status is shown in the taskbar (at the left of the clock).
Simply tap the battery icon for more information.

The unit also indicates the charge status with the LED on its front panel
(see LED Indicators Description on page 8).
C
AUTION
For the four-slot units: Only charge the batteries with the AC
adapter/charger provided by EXFO with your unit.
For the eight-slot units: These units can be connected to the AC
power using a standard three-wire power cord.