How To Properly Charge An Electric Bike
Electric bikes depend on the energy stored in their onboard batteries for Pedal-Assist and Full-Electric ride modes.
When the battery is discharged, one has to recharge it again. However, charging high-capacity lithium-ion batteries is not just plug-and-play since one has to take into account many little details.
Published: February 17, 2023.
Intro to Electric Bike Batteries
Electric bike batteries are almost exclusively lithium-ion batteries due to their energy-to-weight and power-to-weight ratio - they are lighter than Nickel Metal Hydride batteries, feature no memory effect, can provide rather strong currents, accept the charge well, etc.
However, lithium batteries are very sensitive to charging conditions and must be recharged using the lithium battery chargers that came with the electric bike.
When lithium-ion batteries are not charged properly, they can easily overheat, catch fire and even explode.
To prevent such issues, some electric bike batteries come with Battery Management Systems (BMS), which protect the batteries from harmful events like overcharging, over-discharging, short circuit, over-current, low and high temperatures, etc.
However, not all electric bike batteries feature BMSs.
Electric bike batteries can be charged while being disconnected from the bike or while still being attached to the bike.
Also, there are a few things one can do to help the battery perform at its best.
How To Charge Removable Electric Bike Battery
Remove the battery from the bike
- Power off the bike to deactivate the battery,
- unlock the battery using the battery key, and if the bike features holding tabs and clips, unlock them as well,
- remove the battery from the bike.
Some electric bikes require users to remove the bike seat before the battery can be removed - in that case, perhaps it is easier to charge the battery while still being connected to the bike.
Charge the battery
Before charging the battery, verify that the battery is clean and dry and that it is not very warm from the previous ride - if the battery is very warm, let it cool down for at least 30 minutes.
Plug the battery charger into the electric outlet and then plug the battery charger into the battery.
Observe the diagnostic LEDs on both the battery and the charger - if everything is good, let the charger charge the battery.
Charging time depends on the battery's discharge level and the charging time of the empty battery.
For example, if the charging time of the fully discharged battery is 5h, the battery discharged down to 50% will be fully charged in 2.5-3h.
When the battery is fully charged, disconnect it from the battery charger - some batteries and their chargers allow the users to leave the battery connected to the battery charger indefinitely, but just in case, when the battery is fully charged, disconnect it from the charger and disconnect the charger from the electric outlet.
Attach the battery to the ebike
After the battery is fully recharged, attach the battery to the bike - slide it back into its slot, lock it properly, and turn on the bike to verify that everything is alright with the battery and electric connections.
How To Directly Charge Electric Bike Battery
Directly charging the ebike battery is very similar to the previous method.
Before charging the battery, verify that the battery is clean and dry and that it is not very warm from the previous ride - if the battery feels very warm, let it cool down for at least 30 minutes.
- Place the ebike in the vertical position, turn it off, and locate the battery charging port.
- Plug the battery charger into the electric outlet and then into the battery.
- Observe diagnostic LEDs while the battery is being charged - if there are no alarms of any kind, let the battery charger fully recharge the battery.
- When the battery is fully recharged, disconnect the battery charger from the battery and then from the wall outlet.
- Turn on the ebike and verify that everything is alright with the battery.
- Before the next ride, let the battery cool down for at least 30 minutes.
Second Battery - Yes or No?
Since modern electric bikes feature batteries that may be fully recharged anywhere from 3 to 6-7 hours, many riders wonder if they should get a second battery for their bike.
Having a second battery brings many benefits, including:
- The rider can use the ebike with one battery while the second battery is being charged.
- When going for longer rides, one battery can be attached to the bike, while the second battery can be used when the first one is discharged, practically doubling the range.
- Having a second battery allows the rider to let the batteries cool down before and after the charging since there is less need to charge the second battery as quickly as possible, etc.
However, batteries for electric bikes are not cheap, so having the second one requires some money to be spent.
Electric Bike Batteries Frequently Asked Questions
Here are some of the most popular Frequently Asked Questions about ebike batteries.
How to charge an electric bike?
Electric bike batteries are charged using lithium battery chargers that are recommended/provided by the battery manufacturers.
Charging the battery with other chargers may lead to the battery overheating, fire, or even explosion.
Do electric bikes charge while pedaling?
Some yes, some no - this depends on the ebike model and the onboard battery controller, which may also feature an electric brake, allowing the bike to recover some of the kinetic energy while braking and slowing the bike down.
Should I charge my ebike battery after every ride?
Lithium batteries don't suffer from the memory effect and can be recharged even when not fully discharged.
However, be sure not to let the battery stay connected to the battery charger too long, and always let the battery cool down before (if required) and after the charging.
Periodically it is a good practice to discharge the battery (almost) completely.
How long does an electric bike battery last?
Depending on the battery use, quality, quality of the charger, etc. ebike battery may last up to 500-1000 charging/discharging cycles.
Some Lithium Iron Phosphate (LiFePO4) ebike batteries with built-in BMS may last 1000+ cycles easily if they are regularly discharged down to at least 20% SoC and if they are not used in too hot and too cold weather.
How much does it cost to charge an ebike battery?
If we assume the price of electricity of $0.15/kWh, a battery capacity of 500 Wh, and a battery charger efficiency of 85%, then the price of a single battery charge is:
$$$ = 0.15 * 0.5 / 0.85 = ~9 cents
This isn't much for a 20-25 miles ride in Full Electric Mode which can be extended to 40+ miles in Pedal-Assist Mode.
How to store an electric bike battery?
If You don't plan on using your electric bike for a few weeks or even months, store the battery charged at 50% SoC at room or somewhat lower temperature - there is no need to store it in the fridge, for example.
Before the next use, recharge the battery at 100% and use it as usual.
What are the most common mistakes that kill lithium batteries?
Lithium batteries are excellent in terms of capacity and power but are also rather sensitive to certain conditions:
- Since they don't feature a memory effect, there is no need to discharge them every time to 0% SoC (100% DoD). Discharge them to 20-25% SoC and recharge quickly up to 90-95%.
- Don't charge them while they are still hot/very warm after use, and don't use them if they are still very warm after charging. If they are very warm or even hot after charging, check the charger and battery - lithium batteries should be warm after charging, but not hot.
- Don't let the battery freeze in winter, and don't let it "cook" during hot summer days.
- Always use a proper battery charger. After charging, unplug the charger from the battery.
- If You charge the battery after each ride, charge it up to 85-95%, there is no need to top off the battery every time.
When is it time to replace the ebike battery?
When the battery capacity drops down to ~80% of its nominal capacity, it is time to replace the battery with a new one. Old battery should be recycled properly.
What to do if the lithium battery gets extra hot?
Lithium batteries should NOT get hot, especially not extra hot - if the battery was charging, unplug the charger from the wall and try to unplug the charger from the battery.
If possible, place the battery in a metal pot (bucket, for example, or a large cooking pot, or something similar), filled with sand (if possible) away from people, animals, or any flammable material.
If required, contact the nearest emergency service, explain that You have a (potential) lithium battery fire, and act accordingly.
Note: never, but really never try to fight lithium battery fire with water - lithium reacts with water and creates very flammable hydrogen.