Cycle Life Testing

Starting 2018 I changed my test setup. I switched from SkyRC MC3000 to OPUS chargers. I use BT-C2000 for AA cells (it’s actually everActive NC3000, an OPUS BT-C2000 clone) and OPUS BT-C700 for AAA cells.

AA Cycler - Cycle Life Testing - Test Setup 2018

The new setup uses these cycling currents

Cell Size Charge Discharge
AA 1000 mA 500 mA
AAA 700 mA 500 mA

Note: The charge current on BT-C700 is halved once the cell reaches 1.45V.

With these chargers I can not control the charge and discharge conditions anymore. All I can set is the current. Both chargers discharge to around 0.9V open circuit, I wish it was 0.9V under load.

I use the Refresh function to run 3 discharge-charge cycles at once. When the refresh finishes I write down the capacity, measure the internal impedance with EM3610, and start another refresh cycle.

From the first 24 values I calculate the initial capacity of the cell. I keep cycling the cell until it falls below 80% of its initial capacity.

At the end I calculate the cell’s average capacity and the total Amp-hours it delivered throughout its lifespan (score).

Reasons for change

Switching to OPUS chargers also means I am not able to measure energy (mWh) anymore. I wish OPUS added this feature with a new firmware release.

Old Test Setup (until 2018)

AA Cycler - Cycle Life Testing - Test Setup

The cycling current is 1500mA for AA and 500mA for AAA cells. Charge and discharge currents are always identical.

Charging uses 0dV termination, discharge cuts off at 0.9 V (measured under load).

Internal impedance is measured once every 10 cycles in charged state using internal resistance meters.

From the first 40 values the cell’s initial capacity is calculated. Then the cell is cycled until its capacity falls below 80%.

At this point the average capacity is calculated from values measured throughout the cell’s lifetime.

Also the score points are calculated (Score = Cycles * Capacity / 1000) which represent the total Amp-hours delivered by the cell throughout its lifespan.

For graphing purposes the cell is cycled yet another 80%, e.g. until 64% of its initial capacity.