Quick answer: Most "it's broken" calls we get are one of four things — a battery that isn't charged, a battery that's worn out, a connector that's worked loose, or a throttle that's failed. All four are checkable in about five minutes, and three of the four are a part rather than a new bike.
Work through the checks below in order. They apply to the dirt bikes and the scooters.
Bike under 12 months old? Stop here and talk to us first. Every Kubbi has a 12-month warranty, and if it's a manufacturing fault you shouldn't be buying anything.
Before anything else: three things in sixty seconds
Is it actually charged? Obvious, and it's still the most common answer. A bike that was put away in October with a half-flat battery and left in a cold shed will be properly flat by now. Put it on charge for a full cycle before you conclude anything.
Is the battery connected? Connectors shake loose over a season of riding, and a bike with a disconnected battery behaves exactly like a dead one. Check the connector is fully seated and the battery is secure in its mount.
Is it switched on and out of a lockout? Check the power switch and the speed mode. If there's a key, check it's turned fully.
If all three are fine and it still does nothing, carry on.
Symptom by symptom
Nothing at all — no lights, no response. After the three checks above, this is usually the battery at the end of its life or a failed connection. A battery that has been stored flat through a winter often won't come back. Chargers fail too, and more often than people expect — if you can borrow the right charger for the model, that's the quickest way to tell which of the two it is.
It charges, then dies almost immediately. That's a worn battery, not a charging fault. A battery that takes a charge but can't hold it under load is at the end of its cycle life. Replacing it is a fraction of the cost of the bike and makes an old one feel new.
Rides are much shorter than they used to be. Same cause, earlier on. Before you replace anything, rule out the cheap explanations: cold weather takes a real bite out of range, soft tyres make the motor work harder, and a child who's grown is simply more to carry. If rides have dropped by more than about half in warm weather, it's the battery. There's more on what's normal in How Long Does a Kids Electric Dirt Bike Last on One Charge?
It cuts out under load — fine on the flat, dies on a hill. Classic tired battery. It can also be the controller, but the battery is far more likely and far cheaper to try first.
The throttle does nothing but the bike has power. Throttles are the most-replaced part on any kids' bike — they get twisted hard, thousands of times, by someone who isn't gentle. If there's power but no drive and the wheel spins freely by hand, suspect the throttle before the motor.
The brakes feel soft or spongy. Usually cable adjustment rather than a failed part, and worth doing before every ride anyway. If the lever comes all the way to the grip, stop riding until it's sorted.
Flat tyre. The dirt bikes run air-filled tyres, so they puncture like any bike and take an inner tube. The scooters run solid tyres and can't puncture at all — if a scooter feels wrong at the wheel, it's the bearing or the wheel itself rather than air.
Rattles and new noises. Go round the bolts. Handlebar clamp, wheel nuts, kickstand, fender. A rattle that appears after a few weeks is almost always something that needed nipping up, and catching it early stops it becoming a part.
Where to get the part
Every model has its own parts list, with the individual components rather than a vague "contact us":
K4 parts · K7 Pro parts · K10 Pro parts · K22 parts · S4 Pro parts
Batteries, motors, controllers, throttles, brake levers, chargers, tyres, inner tubes, kickstands and body panels are all there. If you're not sure which part you need, send us a description of what the bike is doing and we'll tell you — we'd rather sell you the right £30 part than the wrong £90 one.
And if the bike is still inside its 12-month warranty, don't buy anything. Get in touch and we'll sort it.
The things that cause most faults
Nearly everything above traces back to one of four habits. None of them is difficult.
Don't store it flat. A lithium battery left empty for months is the single biggest killer of these bikes. If it's going away for the winter, charge it to around half first and top it up every month or so.
Don't store it cold. A freezing shed ages a battery faster than riding does. Bring the battery indoors.
Use the supplied charger. A charger from something else may fit and will not do the battery any favours.
Wipe, don't hose. These bikes are splash resistant, not waterproof. A pressure washer forces water into exactly the places you don't want it — the connectors and the controller.
Frequently asked questions
The charger light isn't doing what I expect. What does that mean?
It varies by model, so check the manual for yours rather than guessing — on the K4, for instance, the light turns green when the charge is complete. If the light does nothing at all when it's plugged in at the wall, the charger is the first suspect.
Can I use a bigger battery to get more range?
No. The battery, controller and motor are matched, and a bigger one isn't a free upgrade — it's a way to damage the bike and void the warranty. If they need more, they need the next bike up. Is It Time to Move Up a Size? covers when that's actually the case.
How long should a battery last?
Two to three years of normal use is a fair expectation, and how it's stored matters more than how it's ridden. A battery that spends every winter flat in a cold shed will not see two.
Is it worth fixing an older bike?
If the child still fits it, almost always. A battery and a set of tyres costs a fraction of a new bike and buys you another couple of seasons. If they've outgrown it, that's a different question.
Can I fit the parts myself?
Most parts are extremely straightforward. And whatever you order, we'll advise on how to replace it — step by step, to make the job as simple as possible. You won't be working it out on your own.
What if I can't work out what's wrong?
Tell us what it does and what it doesn't do — does it have lights, does the wheel turn freely, does anything happen when the throttle is twisted. That's usually enough for us to narrow it down.
The bottom line
Charge it fully, check the connector, check the switch. If it still won't go, the odds are heavily on the battery or the throttle, and both are parts rather than a write-off.
A kids' electric bike that stops working is usually a thirty-pound problem wearing a six-hundred-pound disguise.
Kubbi supplies electric bikes and scooters to over 15,000 UK families. Everything ships from our own UK warehouse with a 12-month warranty and spare parts held in stock.