Editing Battery Refurbishment (section)

== Step 6: Keep the pack electronics alive ==

'''This step is skipped at your peril on smart packs.'''

Some fuel-gauge and protection circuits lose critical calibration data — including the digitised shunt resistor value that the coulomb counter depends on — if their supply is interrupted for even a fraction of a second.<ref name="bu-911" />

The technique is to supply the board from a bench supply at the same voltage through a '''100 Ω resistor''', connected '''before''' the old cells are disconnected, and removed only '''after''' the new cells are in place and supplying the board. The resistor is low enough to keep a digital circuit powered and high enough to protect against an accidental short.<ref name="bu-911" />

The same 100 Ω resistor is the safe way to probe an apparently dead pack. Some packs use a solid-state switch that leaves the terminals at zero volts until it is enabled: with the voltmeter on the outer terminals, tie one end of the resistor to ground and touch each remaining contact in turn, then repeat with the resistor tied to a positive rail, and watch for the pack output waking up.<ref name="bu-911" />

If nothing responds, the pack may be locked by a manufacturer activation code. '''Those codes are proprietary and are not published''' — even to service staff — so a code-locked pack cannot be revived. Some manufacturers also fitted an end-of-life switch that disables the pack at a set age or cycle count.<ref name="bu-911" />