Why does a lithium battery lose capacity?

A lithium-ion battery doesn't fail overnight — it ages gradually through two distinct mechanisms. Calendar ageing happens even without use: the passivation layer (SEI) covering the anode slowly thickens, consuming active lithium. Cycle ageing depends on the number of charge/discharge cycles: with each one, micro-cracks form in the electrode materials and some lithium becomes permanently inaccessible.

For a typical scooter battery (350–500 Wh, usually NMC chemistry), a ~20% capacity loss is common after 500–800 full cycles — often 2 to 4 years of daily use. Beyond that, the decline accelerates because the weakest cells in the pack limit the whole.

Three factors markedly speed up this degradation:

  • Sitting at 100% charge: leaving the battery permanently plugged in at full charge stresses the electrodes. Aiming for 20–80% in everyday use noticeably extends lifespan.
  • Temperature extremes: charging below 0 °C causes irreversible and dangerous lithium plating; storing above 45 °C in direct sun accelerates parasitic reactions.
  • Repeated deep discharges: routinely draining the battery to cut-off wears cells faster than partial discharges.

How to assess your battery's real condition

Before any diagnosis, three observable signals give a first idea:

  • Actual range: compare today's distance to when it was new, under equivalent conditions (mild temperature, same route, same tyre pressure). Dropping below 60% of the original range means at least a third of capacity is gone.
  • Charging behaviour: a healthy battery charges steadily. If the gauge jumps to 100% then collapses within minutes, or shows unstable percentages, the cells are starting to diverge — a sign of advanced imbalance.
  • Abnormal heating: a battery that gets very hot while charging or in use, or that shows any swelling, must be set aside immediately (thermal runaway risk).

These clues remain approximate. Only a workshop test with a charge/discharge bench measures the true SOH (State of Health): the cell is discharged at a controlled current to measure its effective capacity in Ah, then its internal resistance is calculated. That is exactly what cirBATT does on arrival, cell by cell.

Repair, replace or repurpose: the right call

Three questions settle it:

  1. Is the rest of the scooter sound? If motor, controller and frame work, a new battery may be worth it.
  2. Is the pack merely imbalanced, or truly worn? Sometimes a single cell (or a locked BMS) fails the whole pack while the other cells are fine — which is why a diagnosis before discarding matters.
  3. Is a new battery's cost justified? On an entry-level scooter worth €300, a €120–200 new battery often exceeds the device's residual value. Reuse then becomes the most rational choice, economically and ecologically.

Never throw a lithium battery in the bin

It is both illegal and dangerous. A lithium cell crushed in a bin lorry or sorting centre can ignite and trigger a fire that is very hard to extinguish — a real and documented cause of incidents at waste-treatment facilities in France. Mobility batteries fall under the WEEE stream and the Corepile take-back scheme.

Responsible options:

  • A recycling centre with a dedicated WEEE battery collection;
  • Take-back by the retailer (legal "1-for-1" obligation on an equivalent purchase);
  • Drop-off at cirBATT: your battery is tested and, if its cells allow, gives life to a stationary storage pack — with an estimate of its recovery value.

What actually happens to your battery at cirBATT

Your battery is neither shredded nor smelted. It is first disassembled cell by cell. Each cell undergoes a capacity and internal-resistance test; only those keeping an SOH above 70% are retained. They are then sorted into performance-matched groups and reassembled into a new pack fitted with our proprietary BMS, designed to manage reused cells.

The result: a battery bound for the scrap heap becomes the core of a storage system — solar self-consumption for a household, peak shaving for an SME, or backup for an off-grid site. The loop is closed, and value is created where there was only waste.