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How often should batteries be tested?
Trend internal impedance or conductance every 6 to 12 months, and run a load bank capacity discharge test at commissioning, then every 2 to 5 years, moving to annually once the string passes 80 percent of its expected life. Impedance finds weak cells early; only a capacity test proves how many minutes of autonomy remain.
Testing intervals are usually set by whoever last renewed the maintenance contract. Here is what the duty actually calls for.
Recommended intervals
Adjust for criticality: a data center or a hospital tightens every interval, a low criticality office can relax them.
| Activity | Interval | What it proves |
|---|---|---|
| Visual and torque check | Every 6 months | Corrosion, leaks, loose connections |
| Impedance or conductance | Every 6 to 12 months | Weak cells against baseline |
| Thermal imaging | Annually | Hot joints and cells |
| Capacity discharge test | Commissioning, then 2 to 5 years | Actual remaining autonomy |
Why impedance alone is not enough
Impedance correlates with cell health but not directly with capacity. A string can show acceptable impedance across every cell and still deliver only 60 percent of rated capacity, because uniform ageing does not create outliers. Impedance is a screening tool between capacity tests, not a replacement for them.
Keeping the site protected during testing
A capacity test takes the string out of service for the discharge and the recharge that follows, which can be many hours. Plan a temporary battery or a generator standby for the window, agree the end voltage and load profile in advance, and record the results against the commissioning baseline so trending remains meaningful.
Frequently asked
- Does testing shorten battery life?
- A capacity test consumes one deep cycle, which is negligible against a design life of hundreds of cycles. The information gained is worth far more than the cycle spent.
- Can EXBATT test batteries we did not supply?
- Yes. Battery testing and diagnostics is offered as a standalone service for third party sites, including data centers, substations, and telecom operators, with a written condition report.
- What result means the string must be replaced?
- Delivered capacity below 80 percent of rated, or a capacity drop of more than 10 percent between consecutive tests, both indicate replacement should be planned now rather than deferred.