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How High Impedance Affects Rechargeable Batteries
What is high impedance?

Newer, more advanced battery analyzers like the Maha MH-C9000 test more than just the battery capacity. If a battery is unable to maintain a load the Maha MH-C9000 returns a result "HIGH" which stands for High Impedance.

What is high impedance? High impedance is another term for "high internal resistance". This means with age or poor maintenance, a rechargeable battery develops a high internal resistance causing the battery to collapse with heavy current demands. So, while the battery may show a 'full charge' on a volt meter and an acceptable capacity level on an analyzer, when put to the test the battery is not able to sustain the current draw for the application causing a low battery indicator. 

Are all rechargeable chemistries affected by high impedance? Yes, all rechargeable chemistries are affected by high impedance, but not in the same way. NiCad has the lowest starting internal resistance of common rechargeable chemistries, and after a hundred uses it may still maintain a low internal resistance. NiMH batteries start with a higher internal resistance and will develop higher resistance quicker than NiCad batteries, which is why most NiMH batteries have fewer charges available than a NiCad battery. Li-Ion batteries are between NiCad and NiMH, however due to the chemical construction of Li-Ion cells, cell oxidation causes irreversible high resistance with age.

Can high impedance be reversed? Once high impedance reaches a critical level in a rechargeable cell it is almost impossible to recover the cell to a highly useful state. Although with proper reconditioning, NiCad batteries (and in some cases Lead Acid batteries) may recover to a usable state for a brief period. NiCad batteries can be reconditioned with chargers designed to provide a reconditioning cycle.

See all of our Battery Articles.