You can measure it directly with a capacity test, or infer it from how much range you have lost. Either way, this calculator converts it into an SoH percentage, estimates remaining cycles before the 80% replacement threshold, and projects capacity forward from cycle and calendar ageing.
How do you check a lithium battery’s state of health?
State of health is today’s capacity divided by the capacity when new. Measure it with a full discharge test, or estimate it from range on the same route, speed and weather: a scooter that did 40 km when new and does 31 km now is at about 78%. 80% is the conventional replacement point.
Two ways to measure state of health
The direct method is a capacity test: charge to full, ride or discharge at a steady moderate load until the pack cuts out, and record the energy delivered. Divide by rated watt-hours and you have SoH. It takes a full cycle and a wattmeter, but it is the only genuinely accurate answer.
The proxy method is range. If a scooter that reliably did 40 km when new now does 31 km on the same route, at the same speed, in the same weather, you are looking at roughly 78% SoH. The caveats matter — colder weather, higher speeds, lower tyre pressure and a heavier rider all mimic degradation — so compare like with like or the figure will flatter or scare you unnecessarily.
A cold morning alone can mimic 15 points of degradation that are not there, which is the most common reason people conclude their battery is dying when it is merely January.
Cycle ageing and calendar ageing are separate problems
Cycle ageing comes from use. Typical NMC lithium-ion cells are rated for 500–800 full cycles — full to empty and back — before reaching 80% capacity, roughly 0.025–0.04% per cycle. Shallower cycles age cells more slowly, so a well-treated scooter pack that is rarely run flat usually beats its rating. LiFePO4 is dramatically better at 2000–4000 cycles, which is why it appears in fleet scooters despite being heavier.
Calendar ageing happens whether you ride or not, at roughly 2–3% per year at 25 °C and a moderate state of charge — but far faster if the pack is stored hot and full. A battery kept at 100% in a summer shed can lose 6–10% in a single year without turning a wheel. Storage at 40–70% charge in a cool place is the single best thing you can do for a pack you are not using.
| Age and use | Expected SoH | 500 Wh pack holds |
|---|---|---|
| New | 100% | 500 Wh |
| 1 year · 250 cycles | 92–96% | 460–480 Wh |
| 2 years · 500 cycles | 85–92% | 425–460 Wh |
| 3 years · 750 cycles | 78–86% | 390–430 Wh |
| 4 years · 1000 cycles | 70–80% | 350–400 Wh |
When to replace rather than nurse
80% SoH is the conventional end-of-life marker, but for scooters the practical trigger is whether the pack still covers your commute with reserve. A 600 Wh pack at 78% still has 468 Wh — plenty for a 15 km round trip, and no reason to spend money.
Replace when you see behaviour rather than just numbers. Gradual fade is slow and predictable; the signs below are not. They point to a cell-level fault rather than ageing, and unlike fade they do not get better and are not safe to ignore:
- Sudden voltage sag under throttle that was not there last month
- A gauge that reads full, then collapses within a kilometre or two
- One parallel group reading far below the others on a cell-level check
- Any swelling, heat at rest, or a sharp chemical smell
- A BMS that cuts out under moderate load and needs a reset to recover
The last one is sometimes a failing BMS rather than failing cells, which is a cheaper repair. Everything else on that list means retiring the pack. For what to do differently with the next one, see the charging habits guide.
How the calculator works
State of health is today’s capacity — or today’s range on the same route — divided by the figure when new. The calculator then splits the loss in two: the calendar share, from your storage conditions and the pack’s age, and the cycle share, which is whatever remains. Fade per cycle comes from the cycle share, and the projection runs both forward at your current rate of use.
The formula
losscycle = losstotal − losscalendar
fade per cycle = losscycle ÷ cycles
cycles to 80% = ( SoH − 80 ) ÷ fade per cycle
Related calculators
If you read state of health from lost distance, the range calculator helps separate a tired pack from a cold day or soft tyres. Gentler charging slows the decline, and the charge time calculator shows the 80 percent habit that helps most. The watt-hours calculator converts a measured capacity back into usable energy.
Questions riders actually ask
What is a normal state of health after two years?
For a scooter charged daily and stored indoors, 85–92% after two years and 300–500 cycles is typical. Below 80% at that age suggests fast charging, deep discharges, hot storage or cold-weather charging — or simply low-grade cells in a budget pack.
How many cycles does an electric scooter battery last?
Standard lithium-ion packs give 500–800 full cycles to 80% capacity. Partial cycles count proportionally, so charging from 60% to 100% every day is about 0.4 of a cycle, not a whole one — which is why shallow daily top-ups age a pack far more slowly than deep discharges.
Does fast charging really damage the battery?
Yes, measurably but not catastrophically. Charging at 0.5C or more raises internal heat and accelerates the growth of the layer that consumes lithium at the anode. Expect noticeably faster fade if you fast-charge every day; occasional fast charges are not worth worrying about.
Can a battery be rebalanced or recovered?
A pack with drifted cell groups can sometimes be rebalanced by a slow full charge with a good BMS, which can restore a chunk of apparent capacity. Genuinely lost capacity from cycle and calendar ageing cannot be recovered — no charger, additive or firmware update reverses it.
Is it worth replacing individual cells?
Rarely. Mixing new cells with aged ones drags the new ones down to the old pack's behaviour, and mismatched internal resistance creates uneven heating. Replacing an entire failed parallel group with matched cells of the same model is defensible; single-cell swaps in an old pack usually are not.
How should I store a scooter over winter?
Charge to about 50–60%, disconnect if you can, and keep it somewhere that stays between 5 °C and 20 °C. Top it back up to 50–60% every couple of months. Never leave a pack fully charged or fully flat for months, and never charge it while it is still freezing cold.
Sources
Primary and reference sources for the physics, standards and figures used on this page.
- BU-808: How to prolong lithium-based batteriesBattery University
- BU-410: Charging at high and low temperaturesBattery University