The battery is the most expensive part of any electric bike. Treat it well and it'll last 5+ years. Treat it badly and you'll be buying a replacement in 18 months.
Parents often ask us about this when they've just taken delivery, and honestly, if you get the basics right it barely requires any thought. But "the basics" aren't obvious, and doing the wrong thing is pretty easy — especially in an Australian summer where a tin-shed garage hits 50°C by mid-afternoon.
Here's the whole picture, plain-English, from the people who build these bikes.
What's actually in a kids' ebike battery
Every quality kids' electric bike uses lithium-ion cells — either cylindrical 18650 cells (like giant AA batteries, arranged in a grid) or prismatic cells (flat packs). The cells are wired in parallel and series arrangements inside a sealed plastic case, managed by a BMS (Battery Management System) — a small circuit board that monitors every cell.
The BMS does three critical jobs:
- Prevents overcharging — cuts the charger off when the pack is full
- Prevents over-discharging — cuts power to the motor if any cell drops too low
- Balances cells — makes sure no single cell sits at a wildly different charge level than its neighbours, which is what destroys packs over time
Cheap no-name ebikes often skip or skimp on the BMS. Ours don't. That's half the reason quality batteries last 5+ years while cheap ones die in 2.
Beyond the BMS, there's also thermal protection — temperature sensors inside the pack that will shut things down if it gets too hot. These sensors also protect against charging a too-cold battery (yes, that's a thing — charging a lithium battery below freezing can cause permanent damage).
So the battery is more sophisticated than it looks. It's not just a box of cells.
The three things that kill batteries
Virtually every dead ebike battery we see died from one of three causes. Avoid these and you'll get the full lifespan.
1. Deep discharge
Lithium cells hate being run all the way to zero. When a cell drops below about 2.5V (they sit at 4.2V when full), permanent damage starts to happen — the chemistry inside changes in ways that can't be reversed.
The BMS will usually cut power before this happens, which saves the pack. But what kills batteries is storing them at zero or near-zero charge. If a kid rides the bike flat, then it sits in the shed at 0% for three months, the self-discharge of the cells keeps draining them past the BMS cutoff. When you finally go to charge it, some cells are dead and won't come back.
The fix: never store a bike at 0%. If your kid runs it flat, put it on the charger the same day, even for 15 minutes to get it off zero.
2. Overcharge
Modern BMS units are supposed to cut the charger off at 100%. Most do, most of the time. But leaving a battery plugged in for days or weeks keeps it at 100% — and 100% is stressful for lithium cells.
Think of it like rubber bands. A rubber band stretched tight, constantly, eventually loses its stretchiness. A lithium cell held at 100% constantly loses capacity the same way.
The fix: unplug the charger when the indicator goes green. Don't leave it plugged in overnight. Don't leave it on the charger for a week between rides.
Even better: most of the time, charge to 80-90%, not 100%. More on this below.
3. Heat
This is the Australian-specific one, and it's the cause we see most often here.
Lithium cells degrade faster when they're hot. "Hot" starts around 40°C and gets severe above 50°C. A tin-shed garage in summer hits 50°C+ by lunchtime, easily. A bike left in the back of a car parked in the sun gets hotter than that.
Storing a battery at 50°C for a week costs it the equivalent of several months of normal ageing. Storing it there for a whole summer can take 15-20% off its total lifespan.
Charging a hot battery is worse than storing it hot. If the bike's just been ridden hard in 35°C weather, the battery inside is probably sitting at 45°C. Plugging it in to charge straight away while it's that hot adds heat from the charging reaction on top of that, pushing it into real damage territory.
The fix: let a hot battery cool down for 20-30 minutes before charging. Store the battery — or the whole bike — in a cool part of the house or garage, not the roasting spot. If the battery is removable (ours are), bring it inside over summer.
The charging routine that works
Here's what a good charging habit looks like for a kids' ebike:
Between rides:
- Charge to 80-90%, not always 100%. Most chargers hit the green-light "full" point around 95-100%; you can unplug earlier if you're not using the bike that day.
- Only charge to 100% the night before a big ride day — track day, long trail ride, holiday use.
When the ride ends:
- If the battery is hot to the touch, let it cool for 20 minutes before plugging in.
- Don't let it sit at a very low charge for more than a day or two.
When the light turns green:
- Unplug. Don't leave it on the charger for 8 hours extra. The BMS will protect the pack, but not for free — the cells spend that time at 100% which speeds wear.
Weekly, if the bike isn't being ridden:
- Check the charge level. If it's dropped below 30%, top it up to 50-70%.
This sounds like a lot, but after the first couple of weeks it becomes automatic. You plug it in after a ride, you come back in an hour or two, you unplug. That's it.
Storage: short term, long term, Australian summer
Short term (days to a week): Leave the battery at whatever charge level it's at after the ride. Don't worry about it. Store the bike out of direct sun, ideally somewhere that stays under 30°C.
Medium term (weeks to a couple of months, maybe a winter off): Charge to 50-70% before storing. Unplug. Store somewhere cool (under 25°C if possible), dry, and out of direct sun. Check the charge level every 4-6 weeks and top it up to 50-70% if it's dropped. Lithium cells self-discharge at 2-5% per month, so a battery left untouched for 6 months can drop into dangerous territory.
Long term (a full year or more — uncommon but happens): Same as medium term, but check every month. Consider pulling the battery out of the bike and storing it in the house where temperature is stable.
Australian summer specifically: The biggest single thing you can do for battery life is bring the battery inside over summer. All our bikes have removable batteries for exactly this reason. A battery sitting at 22°C on a shelf in the laundry will outlive a battery sitting at 50°C in a tin shed by years.
If the bike itself can't come inside, at minimum pop the battery out and bring it in. Five minutes of work that could save you a $400 replacement.
Warranty and what voids it
FXB covers batteries under our 2-year warranty, which is longer than most Aussie kids' bike brands (many offer 1 year). The warranty covers manufacturing defects and premature capacity loss — if your battery won't hold charge after a year of normal use, that's on us.
What voids the warranty (same as every ebike brand):
- Water damage. Don't dunk it, don't leave it out in heavy rain overnight, don't pressure-wash it. Light rain during a ride is fine. Immersion or heavy sustained water isn't.
- Physical damage. Dropped it off the back of a ute onto concrete? That's on you. Cracked case, bent terminals, dented from impact — not covered.
- Non-standard charger. Use the charger that came with the bike. Third-party fast chargers, car adapters, and "universal" chargers can deliver wrong voltages and destroy cells.
- Tampering. Opening the pack voids warranty and is also genuinely dangerous — lithium fires are bad.
The warranty is there to cover real manufacturing issues, not punishment for mistakes. If you're not sure whether something's covered, email us at hello@ridefxb.au and we'll tell you honestly.
When it's time to replace
Even with perfect care, batteries eventually wear out. Signs it's time:
- Range has dropped 25%+ from when the bike was new. If you used to get 30km and now you get 22km, the pack is tired.
- Charge time has changed. If it's charging much faster than it used to, it means capacity has dropped. If it's charging much slower, there could be a BMS issue.
- Physical swelling. The battery case has started to bulge. Stop using immediately. Swollen batteries are a fire risk. Don't charge, don't ride, contact us for safe disposal and replacement.
- Sudden shutdowns under load. If the bike cuts out mid-ride despite showing charge remaining, individual cells are probably failing.
When it's time, contact us directly. Because we're factory direct, we carry replacement batteries at close to wholesale — much cheaper than buying through a reseller. For most models it's $300-500 for a new pack with full warranty, versus $600-800 if you buy one through a third party. Call 0400 986 352 or email hello@ridefxb.au and we'll sort it.
The short version
- Don't let it sit flat. Charge within 24 hours of a discharge.
- Don't leave it on the charger for days. Unplug when full.
- Keep it cool. Remove the battery and bring it inside over an Australian summer if the bike lives in a hot shed.
- Charge to 80-90% most of the time. Only go to 100% before a big ride.
- Use the supplied charger, not a knockoff.
- Store at 50-70% if you're putting it away for weeks or months. Check it monthly.
Do this and you'll comfortably get 5+ years out of a quality battery. Ignore it and you'll be buying a replacement in 18 months.
Questions? We're at hello@ridefxb.au or 0400 986 352. We'd rather talk to you about battery care now than sell you a replacement pack early.
