Battery knowledge to brag about: 14 facts & 5 myths about the e-bike battery
Adrian Kaether
· 31.05.2025
Battery myth #1
Advantage 48 Volt
Common e-bike systems rely on 36 volt system voltage. Some manufacturers propagate increased efficiency with 48 volts, e.g. ZF and Specialised with the SL system. However, our test did not reveal any significant difference, as many factors play a role in performance. By the way: Even the new DJI Avinox high-flyer motor relies on the supposedly old-fashioned 36 volt system voltage.
Battery myth #2
Batteries explode easily
Experts agree: batteries can explode. But the risk of an undamaged quality battery catching fire is close to zero. This is because several factors have to come together to cause such a drastic malfunction.
Care must nevertheless be taken when handling rechargeable batteries. The greatest danger is when charging damaged batteries. The batteries have an enormous energy density and even if battery fires are very unlikely: They can have devastating consequences.
Battery myth #3: Fast charging harms the battery
Theoretically, it's true: the faster you charge, the higher the battery wear. However, there are hardly any real fast chargers for e-bikes, as there are for cars. The only exception: DJI. And here too, experts say that a charging speed of eight to ten amps has no significant effect on the service life of batteries with 600 to 800 watt hours. Conventional chargers only charge at around four amps, roughly half as fast. Reducing the charging speed even further has almost no effect on the service life. Incidentally, when in doubt, the motor sucks a good four times as much current out of the battery under full load as a standard charger puts in. If you want to conserve the battery, you should start here rather than with charging.
Battery myth #4: The memory effect
Lithium-ion batteries have no memory effect. Unlike previous battery designs, the battery does not have to be completely discharged before it can be recharged. On the contrary: Intermediate charge levels favour battery life. Small intermediate charges can therefore even have a positive effect if long-lasting extreme charging states are avoided.
Battery myth #5: Never drive on empty!
A real deep discharge can damage the battery. But the manufacturers have taken precautions. The electronics in the battery (BMS) still retain a residual amount of energy. So even if the battery announces "empty", it is not completely discharged. The only important thing is: if you run the battery flat, it is best to recharge it to a medium level afterwards. Otherwise there is a risk of deep discharge after a long period of inactivity.
1 What are rechargeable batteries?
The battery is the "tank" of the e-bike. What the often unspectacular outer shell conceals: Inside are true masterpieces of electrochemistry. A standard lithium-ion battery consists of around 50 individual cells, which are shaped like an oversized AA battery. The charging and discharging process of the cells is monitored and controlled by electronics built into the battery: the so-called BMS, short for battery management system.
2 Why so expensive and heavy?
Together with the suspension fork and wheels, batteries are among the most expensive components on an E-MTB. With large batteries, even the motor is cheaper. Why is that? A battery simply contains a lot of expensive material. The individual cells alone cost several hundred euros to purchase and are also responsible for a large part of the weight. The approximately 50 cells for a battery with 800 Wh weigh almost three and a half kilograms together - even without the battery casing and electronics.
3 Watt hours, volts and amps?
Batteries come in different sizes. The amount of energy in an e-bike battery is usually expressed in watt hours (Wh). Battery experts often think in terms of ampere hours (Ah). Both values describe different sides of the same coin and are linked by the battery voltage (volts). For example, a battery with 20 ampere hours and a voltage of 36 volts has 720 watt hours: 20 Ah x 36 V = 720 Wh.
4 Not all rechargeable batteries are the same!
Same capacity, but completely different performance in practice? This is not uncommon with batteries. For example, in our experience, the old 630 Wh battery from Shimano delivers significantly less range than a new 600 Wh battery from Darfon, for example. With the same motor system. The reason for this may lie in the quality of the cells used. The electronics also play a major role. For example, if the BMS retains a noticeable amount of residual charge in the battery to prevent a damaging deep discharge.
5 How far does the battery last?
Every e-bike newbie asks themselves this question! Unfortunately, we can't give a clear answer. This is because the actual range depends on many different factors. In mountain bike use, rider weight and metres in altitude play the biggest role. Larger batteries provide a greater range, but are also heavier. Batteries with 700 watt hours and more make really long tours possible with medium support. If you reduce the motor assistance considerably, you can extend the range even further.
6 The golden 30-80 rule
Modern e-bike batteries rely on lithium-ion technology. These batteries feel most comfortable at medium charge levels. If the battery is stored for longer in a fully charged state, this accelerates ageing. Even a completely empty battery can become a problem. Keyword: deep discharge. It is therefore best to only fully charge the battery directly before riding. For storage, keep the battery level between 30 and 80 per cent.
7 How long does a battery last?
If handled properly, a rechargeable battery will not break down from one moment to the next. However, over time and with each charge and discharge, the liquid electrolyte in the battery solidifies and the capacity of the battery dwindles. As e-MTBs are often only used once or twice a week as sports equipment, the calendar ageing of the battery usually plays a much greater role than the number of charging cycles. However, even with high demands on the remaining capacity, the battery should last at least five years.
8 Freezing cold or blazing hot: what really damages the battery!
E-bike batteries are designed for a temperature range of around ten to thirty degrees. If the battery is significantly warmer or significantly colder, this is not ideal. This can happen in a cold shed in winter or in a warm car in summer, for example. Charging or discharging these very hot or very cold batteries is particularly problematic. The electrolyte they contain solidifies much faster than normal and capacity is lost. A kind of ageing in fast motion.
9 Battery warmer in winter - rubbish?
The dark neoprene covers can be seen again and again in cities, especially in winter. The approach is correct in theory: cold damages the battery! However, if the bike and battery are always in an unheated shed, even the best neoprene protector is useless. Better: at least warm the battery to room temperature before riding indoors. This is also recommended after riding and before charging.
10 Cheaper and better? Replacement batteries from third-party manufacturers
Some things may seem like a good deal: But we can only advise against it! The actual quality of the battery is hardly comprehensible for end customers. This can mean not only less capacity, but above all a significantly poorer battery safety. It is better to use original batteries. These are often available in various trustworthy shops at well below the RRP. If the original batteries are no longer available, third-party batteries may be an option.
11 On the rear rack: battery out?
A double-edged sword. Actually, the following always applies: the battery is safest in the bike itself. However, if you want to save weight on the rear carrier, you can of course do so. The important thing is that the batteries must be safely stowed in the car, ideally in a transport case designed for this purpose. In addition, the exposed contacts on the e-bike should be protected from the weather. Either with the battery cover itself or with neoprene covers, if necessary with waterproof film. Caution: If you are travelling commercially, you must adhere to particularly strict rules regarding battery transport. Therefore, if in doubt, it is better to transport the battery installed.
12 Got wet or dropped: Is the battery now scrap?
Batteries are not raw eggs. The major brand manufacturers in particular take various precautions to protect the batteries from damage. The housings are robust and extensively sealed against moisture. There are even fixed rules for this. For example, a defined drop height and fixed water pressure that the batteries must be able to withstand without damage. If you have any concerns about your battery, you should inspect it thoroughly. Is there any visible damage to the seals or the outer casing? If so, do not under any circumstances connect the battery to the charger without supervision. If in doubt, only an inspection by a specialist or the battery manufacturer will help. Companies such as Bosch offer their own service for this.
13 Can batteries be repaired?
As with third-party batteries, it is better to keep your hands off them. Although there are a few reputable suppliers, the quality of the repair is not transparent for the end user. In case of doubt, there is a safety risk. With older batteries, the benefit is also limited. If, for example, individual defective cells are replaced, the remaining cells are often already significantly aged and the performance of the battery is impaired anyway. It sounds harsh, but if in doubt, it is better to buy a new battery.
14 End of life: disposing of batteries correctly
Due to the risk of fire, e-bike batteries must never be disposed of with household waste. The batteries contain many valuable raw materials and must be recycled properly. Every e-bike dealer must take back old batteries. Some recycling centres also have corresponding offers.
Adrian Kaether
Editor
