Battery chemistry & storage
Enter your chemistry, current state of health, and usage. See a projected timeline for when you'll want to plan a replacement.
How it works
Step 1
Use the state of health calculator if you don't already have this figure from your BMS or a recent measurement.
Step 2
These set the projected degradation rate going forward, assuming your usage pattern stays roughly the same. The degradation vs usage pattern calculator shows how sensitive that rate is to cycling frequency.
Step 3
Start budgeting and researching replacement options a year or two before the projected date to avoid a rushed decision.
Starting from your current measured state of health, this tool projects forward using your chemistry's typical degradation rate at your stated cycling frequency, solving for how many years it takes to compound down to your chosen end-of-life threshold. It's the forward-looking counterpart to the state of health calculator, which only tells you where you stand today, and it works from a similar starting point to the battery lifespan estimator if you'd rather compare two independent projections.
The math holds your current degradation rate steady going forward, which is a reasonable simplification but won't capture a major change in how you use the battery. If your cycling frequency changes significantly, the degradation vs usage pattern calculator can help you see how a different pattern would shift this timeline, an assumption similar to the steady-duty-cycle baseline NREL's energy storage research uses before layering in more complex real-world usage variation.
A lower threshold, tolerating more capacity loss before replacement, pushes the projected timeline out further, while a higher threshold brings it in sooner. Choose a threshold that reflects how much reduced capacity you can actually live with, not just the default figure from a warranty, since your own tolerance may differ from the manufacturer's stated guarantee level. Once you have a rough target year, the monthly budget fit calculator can help you start planning how a replacement would fit into your budget well ahead of time.
If your battery is still under warranty, the warranty capacity guarantee calculator can help you see whether a replacement around this projected timeline might actually be covered. This same real-versus-projected performance question comes up at grid scale too, where the DOE's Office of Electricity tracks actual storage degradation against projected timelines for planning purposes.
Questions
Projecting forward from your current state of health using your chemistry's typical degradation rate and your cycling frequency gives a reasonable estimate of when you'll hit your end-of-life threshold. An LFP battery currently at 86% state of health, cycled daily, might reach a 70% threshold in roughly 6.5 more years.
If your current state of health is already at or below the threshold you set, the battery has effectively reached that point already, even if it's still functioning. Whether to keep using it or replace it at that point depends on how much reduced capacity you can tolerate for your specific use.
Reducing cycling frequency, avoiding extreme temperatures, and using a more moderate depth of discharge can all slow degradation and push this projected timeline out further. The degradation vs usage pattern calculator shows how much cycling frequency specifically affects this kind of projection.
Starting to plan a year or two ahead of the projected threshold gives you time to budget, research current products, and avoid a rushed decision when the battery's performance actually becomes noticeably limiting. Treat this projection as a planning signal, not a hard deadline.