How to Charge Lithium Batteries the Right Way (and Make Them Last Years Longer)
A few simple habits — the 20–80 rule, the right temperature, and how to store a battery you're not using — can double the useful life of any lithium battery. Here's the engineering behind them.
The 20–80 rule: stay out of the extremes
Depth of discharge vs cycle life
| Depth of discharge | Relative cycle life |
|---|---|
| 100% (full) | Baseline (1×) |
| 80% | Noticeably higher |
| 50% | Several times baseline |
| 20% (shallow) | Highest — but needs more capacity installed |
Charge correctly: rate and voltage
Mind the temperature
Storing a battery you're not using
The short checklist
- Cycle within ~20–80% for daily use; avoid routine 0% and 100%.
- Use the correct CC/CV charger for your chemistry; favour moderate charge rates.
- Never charge below 0°C without low-temperature protection; keep cool in heat.
- Store unused batteries at ~50% in a cool, dry place.
- Retire any cell that swells, overheats or won't hold charge.
Frequently asked questions
Should I charge my lithium battery to 100% every time?+
For longevity, no. Cycling within roughly 20–80% extends life significantly. Charging to 100% occasionally (e.g. before a long trip) is fine, but holding at full charge continuously accelerates ageing.
Is it bad to let a lithium battery go completely flat?+
Yes. Deep discharges stress the cell and, if left flat for long, can over-discharge it below safe voltage. Recharge before it gets very low, and store at around 50% rather than empty.
Can I leave a lithium battery on the charger?+
A quality charger/BMS stops charging when full, so brief periods are fine. But keeping a battery sitting at 100% for long stretches still ages it faster — unplug once charged for daily use.
What's the best storage charge level?+
About 50% state of charge, in a cool, dry place around 15–20°C. Top up to ~50% every few months during long storage.
