What Is a Charge Discharge Tester? How Battery Cycling Works

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What is a charge discharge tester? A charge discharge tester is an instrument that repeatedly charges and discharges a battery cell, module, or pack under a programmed profile, while it logs voltage and current. The purpose is to measure how the battery performs over many cycles: how much capacity it holds, how quickly that capacity fades, how its internal resistance changes, and how it behaves at different currents. Keysight describes this process as battery cycling, which means repeatedly charging and discharging a battery to test its performance, lifespan, and efficiency under realistic conditions.

Quick answer

Short answer to what is a charge discharge tester: A charge discharge tester cycles a battery through programmed charge and discharge steps while logging voltage and current, so capacity fade and internal resistance trends can be measured over many cycles.

The core loop: charge, rest, discharge, repeat

This is a different job from a simple battery tester. A handheld battery tester applies a load for a short time and reports a health reading. A charge discharge tester runs a full sequence, often hundreds or thousands of cycles, and records the data at each step. If you want to know whether a single AA cell is low, a battery tester is the right tool. If you want to know how a lithium cell will age under a particular duty cycle, you need a cycler. This guide explains how the instrument works, what it measures, and where it stops being useful.

A charge discharge tester runs a programmed loop. It first charges the battery at a set current, often constant current until a voltage limit is reached, then may hold at constant voltage. It then discharges the battery at a set current until a cutoff voltage is reached. Each full charge and discharge is one cycle. The instrument repeats the loop, and it records voltage and current at each stage.

Keysight’s use-case page says the cycling system charges and discharges cells, modules, and packs through programmed profiles, from constant-current and constant-voltage steps to full drive cycles. It logs voltage and current per channel. The profile is the key to the test. Changing the current, the cutoff voltage, or the rest time changes the result, which is why a cycling report should always state the test conditions.

Why bidirectional power matters

The instrument must do two jobs. It must source current to charge the battery and sink current to discharge it. A single bidirectional unit does both, so the same channel can run the whole cycle without separate chargers and loads. Keysight’s cycling page describes a bidirectional source that supplies current to charge and absorbs current to discharge.

Keysight’s BT2200 datasheet describes its channels as sourcing and sinking bidirectional current, with current ratings shown as plus and minus values. The same datasheet gives module and chassis configurations, including channel counts and current ratings that depend on how channels are paralleled. Those figures describe that platform only, and they should not be taken as typical for every cycler.

What gets measured

The measurements are voltage, current, and capacity. Keysight’s cycling page says the tests monitor voltage, current, and capacity during each charge and discharge phase. Capacity is the charge the battery delivers during discharge, usually expressed in ampere-hours or watt-hours. Cycling data also shows the trend in capacity across many cycles, which is what reveals fade.

Keysight’s Used Equipment guide to EV battery testing lists capacity, direct-current internal resistance (DCIR), self-discharge screening, and electrochemical impedance spectroscopy (EIS) as cell tests that cyclers support alongside basic cycling. It also points to USABC test procedures as a reference for capacity, power, and cycle-life tests. The guide does not give a full procedure, so users should consult the relevant standard for their application.

What cycling reveals

Cycling shows how a battery ages. Keysight’s cycling page says it reveals battery lifespan, charging speed, and depth of discharge. Keysight’s use-case material also ties cycling to capacity fade and rising internal resistance, which are the two trends most cycle studies track. A battery that holds its capacity for a hundred cycles and then drops sharply has a different problem from one that fades slowly, and the cycler’s log is what separates the two cases.

Cycling also supports energy-storage analysis. The BT2200 datasheet describes its station software as managing the test data, and Keysight’s cycling page notes built-in calculations for power, amp-hours, and watt-hours. These let an engineer compare how much energy goes in against how much comes out, which is the basis for efficiency figures.

Regenerative discharge

Many cyclers can return discharge energy to the grid instead of turning it into heat. Keysight’s cycling page says energy recovered during discharge can be returned to the grid rather than dissipated, and it cites recovery of up to 90 percent of energy. The BT2200 datasheet, by contrast, does not mention regeneration, so the feature depends on the model. Regeneration matters for a lab that runs many cycles, because it reduces both heat and power cost. Check the specific instrument’s datasheet before assuming it has this capability.

Charge discharge tester vs battery tester vs load

Three tools are often confused. A battery tester gives a health reading from a short test. A discharge capacity test uses a programmable electronic load at constant current until a cutoff voltage, which Keysight describes as a narrower test than a full cycler. A charge discharge tester runs repeated charge and discharge cycles, with both directions controlled. Choose the tool by the question. A single capacity check is one test. A life study needs the full cycle.

Logging limits

A cycler is built for long records, and that has a cost. Keysight’s Used Equipment guide says cycler logging can miss fast, small events such as contactor transients and inrush, which can occur within microseconds. It also notes that BMS-class logging typically samples voltage about every 100 ms and current about every 10 ms, so it can show averaged views of fast events. A cycler log is excellent for trends and poor for transients. If the question is about a fast fault, add a dedicated high-speed measurement.

Safety

Battery cycling involves stored energy and, for lithium chemistries, the risk of heat and gas. The tester should be set up with the correct current and voltage limits for the cell, with protection against overcharge and over-discharge, and in a location where a failure can be contained. The test itself can be hazardous, so treat the setup as a live energy source. This guide does not cover a full safety procedure. Follow the cell manufacturer’s limits and your facility’s rules before running any cycle.

What to look for when comparing instruments

Start with the battery type and size. A small cell and a large pack need different current ranges and channel counts. Check whether the instrument is bidirectional, since a unit that only charges or only discharges cannot run a full cycle. Check the logging rate if you need fast transients. Check whether regeneration is included, if power cost matters. Then check the software, because the test profile and the data export depend on it.

Frequently asked questions

Is a charge discharge tester the same as a battery charger? No. A charger only charges. A charge discharge tester charges and discharges under a controlled profile and logs the results.

Can it test a single AA battery? Some units can, but a cycler is designed for cells, modules, and packs at larger currents. For a single AA cell, a battery tester or a multimeter-based load check is usually enough.

How long does a cycling test take? That depends on the profile, the cell size, and the number of cycles. Keysight’s EV guide notes that cyclers often have lead times measured in quarters, which says something about the equipment, not the test duration.

How we chose these sources

We opened each source listed below and used only facts it stated. We used manufacturer learning pages, product datasheets, and the Used Equipment knowledge guides, and we did not use retailer listings, forums, or encyclopedias. Where a source was a patent or a search summary, we did not treat it as a citation.

What we could not verify

We could not verify a complete list of cycler measurements, sampling rates, or standards for any specific instrument from the sources used here. The BT2200 datasheet does not state what it logs, and it does not mention regeneration. The 90 percent recovery figure comes from Keysight’s use-case page and applies to the system described there, not to every tester. The USABC procedures are named as a reference, but their contents were not opened in this session. Product recommendations and prices are outside the scope of this explainer.

Related reading

For a simpler health check of a single battery, see how a battery tester works. For how a multimeter reads a single voltage point, see how a multimeter works.

Sources

• Keysight, battery cycling use case (opened 2026-10-28)
• Keysight BT2200 charge-discharge platform datasheet (opened 2026-10-28)
• Keysight Used Equipment, EV battery testing guide (opened 2026-10-28)