Riding an e-bike is fun, effortless, and fast. Charging your battery to full and then watching it drain rapidly over the course of a few minutes of riding, however, is not a fun experience. Even the best and most reliable batteries will eventually start to fail, reducing their power reserves and causing them to drain within a much shorter timespan than you’d like. So what can you do if your e-bike battery doesn’t seem to hold charge?
The most common causes of an e-bike battery not holding charge are improper charging or discharging conditions, improper storage, charging or operating temperatures, or excessive humidity. Most of these problems can be avoided, but not fixed.
Let’s go over some of the most common factors that can cause your e-bike’s battery to drain quickly, what you can do to reduce them, and how you can prove that your battery is the problem and not anything else.
E-bike Battery Not Holding Charge – The Most Common Causes
In most cases, issues related to your battery not holding a charge are related to your BMS, or battery management system. This is a small computer that lives inside your battery that’s responsible for controlling how power is distributed between the individual battery cells. In some cases, your BMS may be faulty or failing. Most of the time, however, it’s actually doing its job perfectly and cutting off the flow of power to and from bad battery cells.
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In either case, if your battery’s internal components are beginning to go bad, the best thing to do is buy a new battery. Electrical experts and specialty shops can replace dead cells in some circumstances, but it’s difficult to get a hold of replacement cells, working with lithium batteries is very dangerous, and you’ll need specialized equipment to disassemble, test, and reassemble your battery. This is definitely the sort of task that you want to leave to an experienced professional instead of attempting yourself after a few minutes of internet research.
In some cases, however, the battery is actually fine. A short or another electrical issue with your bike’s motor or controller might be draining an excessive amount of power from your battery. In rare cases, the motor and controller might be working fine, but your bike is so inefficient at rolling that the motor has to output a huge amount of power, causing it to use all of your battery life in a few minutes.
Finally, there’s a chance that your battery’s issues are related to heat and how you’ve been storing your battery. We’ll dive into that issue first, as it’s the simplest to fix.
Problem: Improper Battery Storage
Batteries do not like extreme temperatures. Not only will your battery perform worse in extreme heat or extreme cold, but exposure to harsh temperatures can massively decrease the lifespan of your battery.
In general, it’s a good idea to try to keep your battery at room temperature at all times. If you live in a hot climate, it’s totally fine to ride your bike around on a hot summer day, but you probably don’t want to leave your bike’s battery out in the sun all day when you’re not riding it. Try to store your bike in the shade if it’s outdoors. If possible, take the battery inside when you’re not riding the bike. Heat usually won’t have an immediate negative impact on how your battery performs, but it will make your battery fail much faster.
If you live in a cold area, extreme cold can make your battery drain incredibly rapidly. Cold tends to be less bad for your battery long-term than heat, but it will massively decrease the performance of your battery. Again, it’s okay to ride your bike outside on snowy days, but you want to avoid storing the battery outside as much as you can. Try to take it inside whenever you can. Unlike on hot days, your battery will likely discharge quite quickly on cold days due to the temperature. There’s not a lot you can do about this other than wrapping something around your battery to insulate it.
Charging your battery in cold temperatures is worse for the battery than being used in the cold. It’s always preferable to bring the battery indoors for a few hours before charging it in the winter.
Excessive humidity is also an enemy of bike batteries because they lead to corrosion, which is why they fail sooner in humid climates than in dry ones.
Of course, the ultimate enemy of the battery is water, which can cause a short circuit and kill your battery in an instant, so you need to protect it as much as you can. Most batteries’ casings provide sufficient protection from rainfall, but if you live in a particularly wet area, you may consider adding some extra protection to your battery when out in the rain.
For example, my Swytch e-bike kit’s battery came with a rain cover to protect it from getting wet.
Problem: Inefficient Bike
E-bikes aren’t always designed with pedaling efficiency in mind. After all, there’s a big electric motor helping you along. In some cases, however, riders will make choices that make their bikes even more inefficient, causing the motor to work overtime, which in turn will drain the battery very rapidly.
The problem isn’t that the battery doesn’t hold charge, but rather that your bike requires too much energy to be ridden, which depletes your battery too fast.
Testing this is simple: try riding your bike around without the motor and see how it feels.
If you’ve got a fat tire e-bike with very low tire pressure, your rotors are out of alignment and rubbing on your brakes, or the bearings are shot in one of your wheels, you’ll notice that the bike is very hard to pedal and that it coasts to a stop quickly.
You can fix some of these things yourself, but if you think you’ve got multiple issues or problems that are beyond your ability to fix them, consider taking your bike to a shop for a tune-up. The professionals will quickly spot all of your issues and probably fix a few that you might not have noticed, giving you a much more efficient bike and a lot more battery life.
Problem: Bike Motor / Controller Electrical Issue
Your motor is supposed to use the electricity in your battery to spin your wheels, but sometimes there’s a short (essentially an electricity leak) that causes it to waste power.
If you think this is the case, the best test is to either try your battery on a different bike or try your bike with a different battery. If your bike drains another battery very quickly, the motor or controller has an electrical issue that’s draining excessive power. If your battery drains quickly in a different bike, the battery is almost certainly at fault.
If you don’t have a spare bike or battery you can test with (and you can’t borrow one from a friend), you can use a voltmeter (or multimeter) on the terminals of your battery to measure the voltage.
You don’t need to disassemble the battery. Look for a number that makes sense based on the voltage of your battery. If it’s within the right order of magnitude but fairly low, you’ve probably got a failing battery. If it’s very close to the nominal voltage, you might want to wait a few hours and check it again. If the level stays similar, you’re probably looking at an issue with your bike.
Problem: Old / Failing Battery
Lithium batteries have a lifespan of about two to three years or approximately 1000 full charge cycles. This means that even with ideal use conditions (no exposure to excessive heat, charging to 80% and discharging to 20%, and storing the battery carefully when it’s not being used regularly), you’re going to have to replace the battery in your bike at least twice a decade.
If your battery is new, it’s a good idea to run through the troubleshooting steps above before you buy a new one. If it’s a few years old, however, it might be a good idea to replace it regardless. Even if your battery doesn’t turn out to be the problem, you’ll have a spare that you can use to extend the length of your rides or go on back-to-back rides while the other battery charges. When your battery does die, you’ll have a spare that you can swap to immediately.
