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Internal Resistance
The Cell Int. Res. status information displays each cell internal resistance when balanced
charging Lithium packs.
Viewing individual internal cell resistance enables you to more accurately evaluate pack
quality and condition. If all cells show a low internal resistance, that’s a good indicator that
the pack can be charged and discharged at a higher C rate. Here are two examples:
A pack rated at 5C and 40–50C discharge may have an internal cell resistance of 2
milliohms. This low resistance allows larger currents into and out of the pack with-out
generating excessive heat.
A pack rated at 2C charge and 20–30C discharge may have 17 to 20 milliohms internal
cell resistance. The higher resistance prevents the pack from charging or discharging as
quickly, and the larger resistance will generate more heat during those operations.
A cell poorly matched to the other cells in a pack will show a substantially different internal
resistance. Also, a cell with high internal resistance compared to other cells may indicate
the cell is weakening, which can degrade overall pack performance.
Be aware that individual cell resistance will vary during charge. This is normal and results
from the different voltages and currents applied to the pack during charging.
Use the GT1000 as a tool, measuring and recording the internal resistance of your packs
over time. Look for trends that would indicate the IR of a cell or a pack is increasing over
time. This is a good indication that the pack is aging or has internal damage and should
be replaced eventually.
For best results, Lithium packs should be stored at 50% of capacity. Use GT1000’s Store
Mode to prepare Lithium packs for storage.
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