ebike battery problem and solutions valk

In this post, we will be looking into how to take care of your e-bike battery, problems, solutions, and quick fixes. It’s a master electric bike troubleshooting guide that will keep your bike running at high capacity for longer.

There is nothing worse than spending hundreds, or even thousands on an e-bike only to have issues with the internal lithium-ion battery or motor down the road.

Ebike batteries are built tough but they are prone to fail prematurely if they are not taken care of. Just like any electrical components they need to be looked after.

How to look after your e-bike battery

electric bike troubleshooting guide

Never charge your e-bike in direct sunlight. Heat will damage the lithium-ion batteries and could fry the charger. Always charge the battery in a cool well-ventilated area out of direct sunlight.

Never fully deplete your e-bike battery. It is best to leave around a 10-20% charge in the battery pack. This will save the internal batteries from going into a low charge state preventing them from being recharged.

Always charge your battery after every use. Lithium-ion batteries will over time lose charge so even if you are not using your e-bike it is best to charge it at least once a month.

Never ride your e-bike through water, rivers, or deep puddles. Even though they are water resistant they may not be waterproof. Water ingress is an easy way to fry your e-bike speed controller, battery, or motor.

How to test an E-bike battery?

How to test an E-bike battery

To test an ebike battery we need to first remove the battery pack from the e-bike. Make sure to turn off the power to the battery pack and unlock it prior to removal. Find the positive and negative main cable terminals which will be providing power to the electric motor.

Put your multimeter on these terminals and check for 36-42V. Some battery packs will not output power unless a signal is sent to the BMS to start up.

Most e-bike battery packs are plug and play which means they are easy to replace if they fail. They are hard to test and repair due to the complex design and tamper-proof screws.

All quality ebike battery cells will be controlled by an electrical circuit called a battery management system or BMS for short. This integrated circuit’s primary function is to charge and balance every 18650 lithium-ion cells in the pack to 100%.

It will also manage a few other tasks like maximum power draw and over-temperature protection. In-built fuses will protect the battery pack if there is a short circuit.

Now to test an e-bike battery we will need access to each individual cell. As they are wired in series and parallel it will be hard to test each one as they are all wrapped into place.

After removing the plastic outer case you can use a multimeter set on DC volts to test each cell. You should get around 3 to 4.2V, any less and you could have a bad cell. Some 18650 battery cells are designed to go as low as 2v before the BMS cuts in but these are special lithium-ion cells. Most BMS will cut in around 2.5V

If you find a 18650 battery cell that is under 2V it is best to replace the individual cell. Although I have successfully repaired some Ryobi 18v battery packs that won’t charge so check out how this was done.

How many 18650 for 36v

There are 10, 18650 batteries for 36v wired in series. For increased power and amps these 10-cell packs are then wired in parallel to complete a battery pack for e-bikes, lawnmowers, and other 36v devices. This will then make 30-40 18650 batteries depending on the application.

My wifes Valk ladies electric bike has 40 lithium-ion cells. So 10 are wired in series and there are 4 strings wired in parallel. The total power is 8.8Ah and each cell is 2200mAh.

How to reset an ebike battery

Ebike batteries can go out on overload or blow an internal fuse for various reasons. Often if they are stressed or overheated they will shut down until the temperature drops to a more appropriate level.

Riding an e-bike up a steep hill with full power will cause the lithium-ion battery to output at maximum amperage. This can cause the battery or electric motor to trip out.

To reset the overload or thermal trip turn off the power to the e-bike and wait 10 minutes for the temperature to drop. Turning off the power will also reset the overcurrent trip.

E-bike battery problems

The following electric bike troubleshooting guide needs to be addressed before use:

  • Swelling of an e-bike battery pack.
  • The E-bike battery not charging.
  • E-bike battery not running for very long.
  • The battery pack is not holding a charge.
  • E-bike not turning on.
  • Electric bike not speeding up.

Swelling of an e-bike battery pack.

If your e-bike battery pack is swelling up you have a serious problem with one or more of the lithium-ion cells. Some ebikes use flat pack cells. These are prone to swelling if they get damaged.

The 18650 lithium-ion cells are much more reliable and resistant to swelling.

If you notice that your battery pack has a bulge in it, turn off the power and remove the battery from the e-bike. It will be a good idea to recycle the battery pack. Most towns and cities will have a place where you can recycle batteries.

Some e-bike batteries are located inside the main (A) frame of the bike, this is harder to spot if there is swelling of the battery pack. The only way to check is to drop the lower plate and remove the battery pack. You will have to disconnect some cables first.

E-bike battery problems

E-bike battery not charging

If your e-bike battery is not charging check the following items.

  • Is the power turned on at the wall outlet?
  • Is the e-bike charger working and outputting over 36V?
  • Has the fuse blown in either the charger or the e-bike battery pack?
  • Is the battery pack hot?
  • Is the battery pack charger port full of dirt or water?
  • Has the battery pack been left discharged for a few months?

E-bike battery not running for very long

The lithium-ion battery has a life of around 700 charge cycles. They tend to lose full charge capacity after 700 cycles. This is normal and will only get worse over time.

Still, if you are charging your e-bike every few days you should get many years out of your e-bike before you begin to notice the battery capacity start to degrade.

If you find that your e-bike battery is not running for very long check the following.

  • Is the battery being charged to 100%?
  • Do you have a disc brake dragging?
  • Is the terrain uphill?
  • Are you assisting the battery by peddling?
  • Are your wheel bearings spinning freely?
  • Do you have a short circuit in the wiring, battery, or motor?

Any one of the above can cause your e-bike battery to discharge very quickly.

The E-bike battery pack is not holding a charge

E-bike battery pack is not holding a charge
Charge the battery pack on the bench if you believe there is a short circuit on your e-bike.

Lithium-ion batteries are very good at holding a charge. But over time like any battery, they will slowly discharge. If your electric bike has not been charged for a few months it is a good idea to give it a quick top-up.

If you find that you are charging the battery but it is discharging fast without being used you may have a faulty battery or a short circuit somewhere.

A quick test to isolate the problem is to remove the battery from the bicycle and charge it up on a bench. Test the battery once it is fully charged and leave it off the bike.

If it holds a charge then the problem will be your e-bike. Most probably a short in the motor or wiring. If it doesn’t hold the charge then you have a short circuit or a bad lithium-ion cell.

How do I know when my e-bike battery is charged?

Your battery charger will often have a LED light that will change its state. Usually, it will go from red to green. In some chargers, the LED light will turn off completely when the e-bike battery is charged.

Be sure to not leave the battery on the charge longer than 24h. Lithium-ion batteries don’t like being left on charge. It won’t hurt in the short term but after a while, the battery will start to degrade and lose capacity.

You will also have an indication on either the battery pack or speed controller of the power level of the battery. This will be 0-100% or a range of led lights.

E-bike not turning on.

e bike charger problems broken cable
Lose cables can cause the e-bike to not turn on

If your e-bike is not turning on check that the main switch is in the on position. Also, check the fuse for the battery. This fuse is often on the side and can blow due to a short circuit, over-current, vibration, or just old age.

If the fuse is good and the battery is charged check that the speed controller is in good condition. Your speed controller is what sends a signal to turn on the battery pack.

These speed controllers can fail if damaged by dropping your e-bike or water gets into them.

Press the on button for 10 seconds to try and force the speed controller to turn on. Some controllers are turned on by pressing the (M) button for a few seconds.

Check that you have at least two bars of power in your battery pack. A very low battery can cause the e-bike to not turn on.

E-bike not turning on.
Press the M button for a few seconds to turn on the e-bike

Make sure that all of the electrical cables are connected tight. Sometimes with mountain e-bikes the dirt roads and jumps can dislodge the connections. Water can sometimes get into these joints. Pull them apart and make sure the connection is tight.

Electric bike not speeding up.

There are a number of reasons your e-bike is not speeding up. Often it is a case of dirty feedback magnets for the proximity switch. These are either located on the pedal crank or the rear wheel hub. Clean them with a rag. This is a very common e-bike battery problem that is often wrongly diagnosed.

Electric bike not speeding up.
Dirty magnets on the crank can cause an Electric bike to not speed up. It is a common problem.

Most quality e-bikes have a switch on the front and back brakes to stop the drive motor. Sometimes these switches can get stuck on and fail. Activate each brake lever a few times to try and free up the switch. A blast of CRC can also lubricate the switch.

You may have to pull the pin out and remove the whole front or rear brake lever to check the limit switch. Another reason why you should not leave your electric bike out in the rain.

ebike limit switch front and rear brake

Check if you are in the correct mode eg: pedal-assist aka pedelecs, throttle control, or pedal only (no electrical assistance). I have often found myself in the wrong mode and I can’t work out why my electric bike is not speeding up.

There is usually a minimum speed that will activate the drive motor which is usually 2-3km/h. This is a safety feature.

What speed are e bikes limited to?

To conform to most road rules around the world e-bikes are limited to 15.5mph or 25km/h. Once the motor reaches its speed limit it will stop providing power. You can still pedal faster than 15.5mph but you won’t receive any assistance from the main drive motor.

Once the speed controller senses that you are under 15.5mph the battery management system will provide power to the motor again. This is a standard feature on most e-bikes to conform to state and country road rules.

Is 250w enough for an electric bike?

Yes in most standard use cases 250w is more than enough for an electric bike to ride on dirt or asphalt roads. I have ridden my Mountain bike up small hills with success using only the 250w motor an 8.8Ah battery. Remember you can always assist the motor by pedaling.

250w drive motors are often limited to 15.5mph or 25km/h and up to 110kg (242lbs) in rider weight.


Electric bikes are the future and they have come a long way. Occasionally I come across some E-bike battery problems while I am out mountain bike riding but it is always a quick fix. Helping out a stranger in need is a very rewarding experience.

Hopefully, the above tips and tricks can help you keep your electric bike running fast and for a long time.

Remember that the biggest danger to e-bike batteries is low voltages and excessive heat. Always keep your battery topped up and your battery will last for a very long time.

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