Can You Overcharge an Ebike Battery?


Electric bicycles, or ebikes, come equipped with a small motor, making it easier for you to pedal up hills and all around town. The motor is powered by a rechargeable battery that must be plugged into a charger and charged before they can be used to power the ebike motor. While charging the battery itself is simple enough, a lot of people worry about what might happen if they overcharge the battery.

Ebike batteries should not be overcharged. Doing so can shorten the battery’s lifespan and can cause it to overheat, which may eventually make it unusable. Fortunately, most modern ebike batteries are built with a smart charging function that makes it impossible to overcharge them.

The rest of this article will discuss the concept of overcharging ebike batteries in more depth, including how and why overcharging is a bad idea and how long you can safely leave a battery plugged in. We’ll also briefly look at how to properly care for your ebike’s battery.

How Would You Overcharge the Battery?

Ebikes most commonly come equipped with a lithium-ion (Li-ion) or a lithium-ion polymer (LiPo) battery, but some also have a lead-acid battery (SLA), a nickel-cadmium battery (NiCd), or a nickel-metal hydride battery (NiMh). All battery types must be charged before and between uses.

To charge any rechargeable battery, plug it into a charging device; one will have been included with your ebike. To overcharge the battery, you would leave it plugged in until the battery’s charge surpasses 100%.

Most modern batteries can’t truly be overcharged. They are designed to cycle off and stop charging once they reach full capacity.

However, the energy in a battery will slowly discharge on its own, even without being used.  If the battery is left on the charger, it will resume charging again once the stored energy drops below a certain threshold. If you make a habit of leaving the battery on the charger past 100%, this on-again-off-again cycle may eventually serve to lower the battery’s overall energy capacity.

A couple easy options to fix the habit of leaving your battery in the charger too long. 

  1. Get a smart plug or smart power bar.  These allow you to control the plug with your phone or app, to turn the power on/off, or set a timer to turn off the power after a certain amount of charging.
  2. If you know how long it takes for your battery to charge fully, you could get an even simpler device – a plug timer.  Simply set the time for charge and the amount of time your battery will sit with an active charge will be just enough and no more.
  3. Or if you can remember, just set a reminder on your phone each time you charge your battery.

What Effect Does Overcharging Have on Ebike Batteries?

If you tend to forget to take your battery off the charger, rest assured that you are probably not doing any major damage. Overcharging isn’t great, but modern batteries are built to withstand it; you’re not going to cause it to overheat and melt or even explode, as you might fear.

Battery Lifespan

The actual lifespan of an ebike battery depends on what specific type it is, the size of the battery, how often the ebike is used, and how the battery is cared for.

Most battery lifespans, however, are referred to in terms of charge cycles. One charge cycle means the battery has used an amount of energy equal to 100% of its total capacity, although not necessarily all at once. If you use 60% one day, fully recharge the battery, and then use 40% the next day, that is considered one full charge cycle.

The lifespan of a battery, then, is how many charge cycles the manufacturer estimates a battery can go through before it starts becoming noticeably less efficient.

Most Li-ion type batteries last 2-5 years and can often hold up through somewhere around 1000 charges, sometimes less and sometimes more. An SLA battery is supposed to last for 200-300 charge cycles, although many users report that battery life starts to noticeably decrease after 100 charges. NiCd batteries often have around 500 charges, while NiMH batteries often have closer to 400.

Check the manufacturer’s guide for your ebike to find out the specifics for your particular battery.

The most common, noticeable effect of frequently overcharging your ebike’s battery is on the battery’s lifespan. When the charger cycles on and off repeatedly, it can ultimately affect the battery’s overall energy capacity. The distance you can go on a fully charged battery will decrease gradually over time regardless of your charging habits, but overcharging will cause this to happen more quickly.

Other Risks

Many people worry that overcharging an ebike battery is actually physically dangerous. It seems like we’ve all heard horror stories of rechargeable batteries getting so overheated that they actually melt. But is there any truth to these kinds of stories? Does overcharging put you at risk of fires or explosions?

In short, no. Remember that nearly all modern ebike batteries have smart charging systems in place that prevent it from actually overcharging; the charging system shuts down once the battery reaches 100% energy capacity. Likewise, these smart charging systems will stop charging if the battery reaches a certain temperature.

It’s important to remember that the occasional faulty battery may be prone to overheating. And using a specially-designed fast charger, which uses a higher amperage than a slower charger, could also overheat the battery. Remember that you can always test the battery for overheating with your finger; it’s okay if the battery feels warm to the touch, but it should not feel hot.

Even if a battery does start to overheat, it’s unlikely that it’ll get hot enough to melt, explode, or otherwise cause property damage, as the charger will automatically shut down. Repeated overheating can still shorten the battery’s lifespan by reducing the overall charge capability, though.

Are There Ever Advantages to Overcharging the Battery?

It is not recommended that you ever try to purposely overcharge an ebike battery for any reason. Any advantages you think you might get in added power or extra distance are far outweighed by the risks of overheating.

How Should I Care for the Battery?

It’s important to take the time to learn how to properly charge, store, and care for your ebike’s battery. Always start with the manufacturer’s guide for specific information, but we’ll talk a little about some general guidelines in the video below:

Charging

To charge your ebike battery, simply attach it to the charging device that came with your ebike. Batteries can be easily removed from the bike for charging, and many can be charged while still on the bike. Don’t cover the battery with anything while it’s charging.

Make sure both the battery and the bike are on a dry, non-flammable surface and stored away from any sources of heat or humidity. Don’t charge the battery in extreme conditions; below-freezing temperatures or high heat can damage the battery. Ideally, charge your battery in a room between 40-70°F (5-20°C).  More about the highs, lows, and max temperatures for ebike batteries.

Most of the time, you’ll need to fully charge the battery before using it for the first time. It’s unnecessary to completely run the battery down before recharging; however, you can go for a short ride and then recharge it after, leaving it fully charged and ready to go again the next day.

But don’t feel like you have to keep it at 100%, either. In fact, most battery manufacturers recommend keeping the charge anywhere between 20% and 80%.

Remove the battery from the charger once it’s fully charged. Smart charging systems may prevent the battery from overcharging, but leaving them plugged in still isn’t good for them, as the charger will cycle off and on as the battery naturally discharges on its own.

Storage

Just as extreme temperatures aren’t good for charging, they’re also not good for battery storage. Like with charging, an ebike battery should be stored in temperatures that are neither too hot nor too cold, somewhere between 40-70°F (5-20°C).  More info on ideal temperatures for ebike batteries here.

For long-term storage, remove the battery from the bike and store somewhere where the temperature will remain within that ideal range. Remember to charge the battery every few months as needed since discharge will happen naturally and it’s best not to let the battery run all the way down to empty. It’s best to store the battery with a charge of somewhere between 40-50%.

Conclusion

In summary, keeping your battery sitting on the charger for long periods of time isn’t great, but overcharging is generally not dangerous. Modern batteries are built to withstand the typical charging scenarios that people have so you’re not going to cause it to overheat, but try to keep the battery off the charger for long periods of time, or cut the power to the charger to make things easy.

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