EXFO FTB-1 - Manual (Page 194)

Maintenance
184 FTB-1
Recharging the Main Battery
To recharge the main battery:
Connect the unit to a power outlet using the AC adapter/charger. The
charge cycle will start and end automatically.
I
MPORTANT

Batteries are not charged at the factory. Install the battery
compartment on your unit (see Replacing Batteries on
page 188), and then fully charge the battery before using the
unit for the first time. The battery is fully charged after a few
hours or when the battery LED indicator stops flashing.

The time required to charge batteries depends on various
factors such as the type of modules currently in use and the
ambient temperature.

To ensure that batteries function or charge properly, keep them
in temperatures between 10 °C and 40 °C (50 °F and 104 °F).
Store below 50 °C (122 °F).

Depending on the way the unit is used, after a while, the charge
status icon may no longer correspond to the actual power level
of the battery (for example, icon indicates that power level is
sufficient, but unit turns off because battery is too weak). A
complete calibration cycle will be necessary (see Recalibrating
the Battery on page 185).