- Stop charging at 80 to 90% for daily riding. Charge to full only when you need the range.
- Store at roughly half charge, never full and never empty.
- Let a hot pack cool before charging, and never charge one that is below freezing.
- Heat and time do more damage than cycles do. A pack sitting full in a hot garage is aging fast while doing nothing.
- Charge where a fire would not spread. Not overnight, not next to the door you would run out of.
Every lithium pack is on a countdown from the day the cells are made. You cannot stop it. What you can do is stop stacking the four things that speed it up, and that is worth hundreds of cycles over the life of the bike.
How packs die
There are two clocks running. Cycle aging is wear from charging and discharging. Calendar aging is wear from simply existing, and it runs whether you ride or not. Most riders obsess over the first and ignore the second, which is backward for anyone whose bike sits five days a week.
Cells wear fastest at the ends of their range. The middle of the charge window is the comfortable part, and a pack that spends most of its life there will outlast an identical pack that lives pinned at 100% or repeatedly dragged to zero.
The four habits
1. Charge to 80 to 90% for normal riding
The last 10 to 20% of a charge is where cells sit at their highest voltage and take the most stress. If your ride does not need the range, do not put it in. Most chargers do not offer a partial setting, so this means unplugging on time or using a charger that does.
2. Do not park it empty
A pack left near zero for weeks can drift below the voltage where a charger will safely restart it. At that point you are not looking at a slow charge, you are looking at a pack that may be finished. If a ride ends low, put some charge back in before it goes on the shelf.
3. Let heat out before you plug in
A pack that just came off a hard ride is warm inside even when the case feels fine. Charging on top of that heat stacks two stresses at once. Give it time to come down to room temperature first. The number of minutes depends on the ride and the weather, and there is no harm in waiting longer.
4. Charge more often, shallower
Two half charges are gentler than one full drain and refill. If you can top up mid-week instead of running the pack down and filling it, do that.
Charge target calculator
Chargers cut off by voltage, so if you want to stop at 80% you need to know what 80% looks like on your pack. Enter your cell count and pick a target.
Charge target voltage
Cell count is the "S" number on your pack. A 72V nominal pack is usually 20S.
Resting voltage, measured at least 30 minutes after charging stops. Voltage read while charging or right after reads high.
Based on standard lithium-ion resting voltages. Your BMS may cut off slightly differently. If the numbers disagree, trust the BMS.
Storage
Storage is where most of the avoidable damage happens, because nothing seems to be going wrong. Cool and half full is the whole rule.
| Time off the bike | Charge to | Where | Check |
|---|---|---|---|
| A few days | Wherever it is | Indoors, off the concrete | Nothing |
| 2 to 4 weeks | 60% | Cool, dry, out of the sun | Voltage before you ride |
| A season | 50% | Indoors, stable temperature | Voltage monthly |
| Over winter | 50% | Never an unheated shed or a car | Monthly, top up if it drifts low |
A monthly calendar alert to check pack voltage is the cheapest battery upgrade there is. Packs that die in storage die quietly, and always between the last time you thought about them and the first warm weekend.
Cold and heat
Cold
Never charge a pack that is below freezing. Charging a cold lithium cell plates metal inside it, and that damage is permanent and invisible until the pack starts behaving strangely. Bring it inside, let it warm to room temperature, then charge.
Riding in the cold is fine, with the caveat that range drops noticeably and comes back when it warms up. A cold pack that seems weak is usually not damaged, just cold.
Heat
Hot is worse than cold for lifespan. A pack in a closed truck bed in summer sun sees temperatures well past anything the ride will do to it. If the bike is stored where the afternoon sun lands, move the pack, not the bike.
Charging safety
- Charge on a hard, non-flammable surface. Concrete floor, not a workbench covered in rags.
- Never charge unattended overnight, and never in a hallway or doorway you would need to escape through.
- Use the charger made for your pack. Voltage and connector matching is not a suggestion.
- Stop immediately if a pack is swollen, hot, hissing, or smells sweet or sharp. Get it outside, away from anything that burns, and do not put water on it.
- A pack that has been crashed hard or punctured is not a pack anymore. Do not charge it to see what happens.
Lithium fires are fast, hot, and very hard to put out. Everything above is written by people who would rather be boring than sorry.
When to retire a pack
| What you see | What it means | What to do |
|---|---|---|
| Range down noticeably from new | Normal capacity fade | Keep riding. Adjust expectations, not the pack. |
| Voltage drops hard under throttle | Rising internal resistance, cells aging | Have it load tested. Plan for replacement. |
| One charge lasts days, the next one hours | Cells drifting out of balance | Full charge to let the BMS balance. If it repeats, get it looked at. |
| Case swollen or deformed | Cell damage | Stop using it now. Do not charge it. Recycle through a proper facility. |
| Charger will not start a charge | Pack below safe restart voltage | Do not try to force it. Tech only. |
Old packs do not belong in household trash or a scrap bin. Call a battery recycler or a shop that takes them. Most do, and most do it free.
Gear in this guide
72V 12A Fast Charger with Charge Display
