Battery chemistry & storage
Enter your warranty terms and a measured capacity reading. See whether it meets the guaranteed minimum for how long the battery has been in service.
How it works
Step 1
You need the original rated capacity, warranty length, and guaranteed end-of-term percentage, all of which should appear on your battery's warranty certificate alongside the terms covered in the warranty capacity guarantee calculator.
Step 2
Use your monitoring app's state of health figure where available. The state of health calculator can help if you only have a raw energy measurement.
Step 3
If your reading falls below the guaranteed minimum, contact your installer or manufacturer with your reading and installation date to start a claim.
Most warranties don't guarantee a flat percentage for the whole term, they guarantee a declining minimum that starts near 100% at installation and reaches the stated end-of-term percentage, commonly 70% or 80%, by the final year, covered from the sizing side in the warranty capacity guarantee calculator. The shape of that decline varies enough between manufacturers that it's worth cross-checking your own document against the warranty coverage value calculator for a sense of what's typical. This tool interpolates that line to find what's guaranteed at your specific point in the term.
A battery can fall below its guaranteed minimum well before the warranty term is up if it degrades faster than the typical curve assumes, which is exactly the scenario this tool is built to catch. Checking periodically throughout the warranty term, not just near the end, gives you the best chance of catching a legitimate claim early, the same reasoning behind the periodic performance validation the DOE's Office of Electricity recommends for grid-scale storage assets under long-term contracts.
This comparison is only as good as the measured capacity you enter, so use a reading from your system's own monitoring rather than a rough estimate. Getting that measurement right is a nontrivial problem, one NREL's residential battery experimentation platform studies directly by comparing consumer battery performance readings against controlled lab measurements. The state of health calculator can help convert a raw energy measurement into the percentage figure this tool expects.
If your battery is meeting its guarantee for now but you're curious how long that's likely to hold, the end of life threshold calculator and replacement timing by chemistry tool can help project further ahead. If you're tracking an inverter warranty alongside the battery, the inverter warranty value calculator runs the same kind of check on that component.
Questions
Compare a recent measured capacity reading against your warranty's guaranteed minimum for how many years the battery has been in service, since most warranties guarantee a minimum percentage of capacity at each point along a declining curve, not just at the very end of the term. If your measured capacity falls below that point's guaranteed minimum, you likely have grounds for a claim.
No, most warranties guarantee a declining minimum that starts near 100% and drops toward the end-of-term threshold, commonly 70% or 80%, by the final year. This tool interpolates that declining line to find the guaranteed minimum at your specific number of years in service.
Most modern battery systems report a state of health or usable capacity figure through their monitoring app or BMS, which is generally the most reliable source for this measurement. The state of health calculator can help if you have a raw energy measurement instead of a percentage figure.
Contact your installer or the manufacturer directly with your measured capacity reading and the date of your original installation, since this is generally the documentation needed to start a warranty claim. Keep a record of your reading and the date you took it, since warranty processes often require this kind of evidence.