Battery capacity is a crucial factor when purchasing an eMTB. However, many bike manufacturers aren’t entirely honest about the actual capacity of their batteries. In this article, we’ll explore the impact of this issue, and explain why manufacturers are somewhat compelled to manipulate figures, and why we advocate for a unified standard.
The debate about battery capacities has been a heated one since day one in the eMTB segment, and still remains one of the biggest selling points for bike manufacturers – as our annual reader survey also confirmed. This makes it all the more important for manufacturers to stay competitive and keep up with current developments. Initially, batteries were mostly mounted externally; today, they’re integrated into the frame and often removable. Nearly all e-bike systems also offer the option of adding an external range extender. Moreover, there has never been such a wide variety of different battery capacities as there is now. As e-bike rider types are becoming more diverse, manufacturers are trying to keep up and cater to the varying needs of different customer groups. Needless to say, bike realised that different different bike- and rider-types require different battery capacities. In other words, consumers are no longer limited to a single battery size, which was the case for a long time due to a lack of options – today, you can get many bike models with different battery options. Pretty cool!
In addition, battery capacities have grown significantly over the years to keep pace with increasingly powerful motors. The common enemy: range anxiety. At the same time, cell technology has improved, allowing engineers to squeeze more battery capacity into the same pack size. This is particularly important for eMTBs, where handling and design are crucial criteria. As a result, pack size, battery shape, and energy density are critical factors – and this is precisely where the problem lies.
Trying to take a critical look at manufacturers’ battery capacity specifications – typically given in watt-hours (Wh) – might bring back memories of your last contract with an internet provider. Most people are aware that the advertised network speeds are rarely achieved, as they are conveniently labeled with an “up to” disclaimer. With e-bike batteries, however, this isn’t the case, even though the underlying concept is quite similar.
The problem: Since there are no specific regulations on how manufacturers have to calculate battery capacity, significant differences can arise between brands – even when the actual capacity is the same. Tolerance ranges are pushed to the limit, standardised lab measurements are recontextualised because they supposedly don’t reflect real-world eMTB scenarios. As a result, varying definitions of how much capacity is truly available to power the motor result in confusing figures. When combined with technical factors such as cell quality, the topic becomes so complex that even experts often struggle to keep up. Some manufacturers take advantage of this complexity. While the figures frequently presented as marketing claims aren’t outright lies, they don’t fully reflect reality – and manufacturers are well aware of this.
Warning, things are about to get technical: In this article, we’ll focus on calculating a battery’s nominal capacity. Nominal capacity can be determined from standardised measured values that every manufacturer is required to provide. This allows not only users but also manufacturers to make fair comparisons. As a result, many bike brands are calling for nominal capacity to become the new standard for specifying battery capacities. While many manufacturers already follow this practice, others still take advantage of buyers’ lack of knowledge by inflating their marketed battery capacity with undefined claims.
How do you work out the nominal capacity of an e-bike battery?
Calculating a battery’s nominal capacity isn’t rocket science, and anyone can work it out in no time. Every battery manufacturer is required to provide the necessary data directly on the battery itself. All batteries have a nameplate displaying various technical specifications. Additionally, manufacturers often include a battery data sheet on their websites, or in some cases, the information is displayed directly on the website, as is the case with Bosch.
Motor manufacturers like Bosch, SRAM, Fazua, TQ, and DJI rely on a closed system, meaning that anyone using their motors must pair them with their batteries. As a result, bike brands have little to no influence over the advertised battery capacity. It’s a different story with motor systems from manufacturers like Shimano and Brose, which allow bike brands to pair their drives with third-party batteries, for example from companies like Chinese manufacturer Trendpower or Taiwanese supplier Darfon. This allows them to influence not only the cell types, cell arrangement, and the matching housing but also the specified battery capacity. Popular examples include Orbea, Canyon, MERIDA, and Specialized, all of which have bikes in their portfolios with custom batteries.
To calculate the nominal battery capacity, you need two values: The first one is the battery’s rated capacity, which is measured in Ampere-hours (Ah). The rated capacity cannot technically be manipulated, as battery manufacturers are required to specify this value according to the IEC61960 standard. It is measured in a standardised laboratory process and reflects the minimum capacity of a cell based on the Gaussian normal distribution. In a nutshell, after determining the average value from the lab measurements, you subtract the tolerance value to find out the minimum guaranteed cell capacity. The only issue – and the reason why manufacturers “technically” can’t cheat – lies in the certification requirements for different markets. In South Korea, for example, certification requires the “rated capacity” to reflect the minimum capacity value. Other markets would accept the actual average value. However, since nearly every cell and battery manufacturer includes the Korean market in their sales strategy, the rated capacity listed on the nameplate always represents the minimum capacity value. This still leaves room for cheeky manufacturers to interpret the numbers differently.
The second value needed is the system voltage, which is measured in volts (V). Most motor systems currently available on the market, like the Bosch CX Gen4 and Gen5, the Shimano EP801, SRAM Powertrain, and Brose Drive S Mag – which is specced on the latest Specialized Levo model, for example – use a 36V voltage system. In contrast, the TQ HPR 50 system operates at 50.4V, the Fazua Ride60 system at 43.2V, and the Specialized SL 1.2 at 46.8V.
All this information can also be found on the battery’s nameplate. To determine the nominal battery capacity, simply multiply the nominal capacity by the system voltage. To prevent you from having to search the internet or run straight to your garage, we’ve done the research for you and compiled a list of all relevant, exciting, and widely-used battery options.
| Brand/Battery | Rated capacity | System voltage | Nominal capacity | Claimed capacity | Deviation between nominal and claimed capacity |
|---|---|---|---|---|---|
| SRAM Powertrain 250 Wh (Range-Extender) | 6,7 Ah | 36 V | 241,2 Wh | 250 Wh | 3,65 % |
| SRAM Powertrain 630 Wh | 16,7 Ah | 36 V | 601,2 Wh | 630 Wh | 4,79 % |
| SRAM Powertrain 720 Wh | 19,6 Ah | 36 V | 705,6 Wh | 720 Wh | 2,04 % |
| Bosch PowerMore 250 (Range-Extender) | 6,7 Ah | 36 V | 241,2 Wh | 250 Wh | 3,65 % |
| Bosch PowerTube 400 | 11 Ah | 36 V | 396 Wh | 400 Wh | 1,01 % |
| Bosch PowerTube 600 | 16,7 Ah | 36 V | 601,2 Wh | 600 Wh | -0,2 % |
| Bosch PowerTube 650 | 16,7 Ah | 36 V | 601,2 Wh | 620 Wh | 3,96 % |
| Bosch PowerTube 750 | 20,1 Ah | 36 V | 723,6 Wh | 750 Wh | 3,65 % |
| Bosch PowerTube 800 | 22,2 Ah | 36 V | 799,2 Wh | 800 Wh | 0,1 % |
| Shimano BT-EN604-A | 11,6 Ah | 36 V | 417,6 Wh | 418 Wh | 0,1 % |
| Shimano BT-EN605-A | 14 Ah | 36 V | 504 Wh | 504 Wh | 0 % |
| Shimano BT-EN606-A | 17,5 Ah | 36 V | 630 Wh | 630 Wh | 0 % |
| TQ 160 (Range-Extender) | 2,8 Ah | 50,4 V | 141,1 Wh | 160 Wh | 13,38 % |
| TQ 360 | 6,8 Ah | 50,4 V | 342,7 Wh | 360 Wh | 5,04 % |
| TQ 580 | 11,14 Ah | 50,4 V | 561,5 Wh | 580 Wh | 3,3 % |
| Fazua 430 | 10 Ah | 43,2 V | 432 Wh | 430 Wh | -0,46 % |
| Orbea Rise (Range-Extender) | 5,6 Ah | 36 V | 201,6 Wh | 210 Wh | 4,17 % |
| Orbea Rise 420 | 11,1 Ah | 36 V | 399,6 Wh | 420 Wh | 5,11 % |
| Orbea Rise 630 | 16,7 Ah | 36 V | 601,2 Wh | 630 Wh | 4,79 % |
| Canyon Trendpower 720 | 19,6 Ah | 36 V | 705,6 Wh | 720 Wh | 2,04 % |
| Canyon Trendpower 900 | 24,5 Ah | 36 V | 882,0 Wh | 900 Wh | 2,04 % |
| MERIDA Trendpower (Range-Extender) | 9,8 Ah | 36 V | 352,8 Wh | 360 Wh | 2,04 % |
| MERIDA Trendpower 600 | 15,99 Ah | 36 V | 575,6 Wh | 600 Wh | 4,23 % |
| MERIDA Trendpower 750 | 19,8 Ah | 36 V | 712,8 Wh | 750 Wh | 5,22 % |
| DJI Avinox 600 | 16,7 Ah | 36 V | 601,2 Wh | 600 Wh | -0,2 % |
| DJI Avinox 800 | 22,3 Ah | 36 V | 802,8 Wh | 800 Wh | -0,35 % |
| Specialized Turbo Levo SL (Range-Extender) | 3,35 Ah | 46,8 V | 156,8 Wh | 160 Wh | 2,05 % |
| Specialized Turbo Levo SL | 6,7 Ah | 46,8 V | 313,6 Wh | 320 Wh | 2,05 % |
| Specialized Turbo Levo | 19 Ah | 36 V | 684 Wh | 700 Wh | 2,34 % |
How bad is the battery confusion really?
This is a question everyone must answer for themselves, as it depends on how much importance you place on actual capacity and how often you fully drain your battery. In most cases, the differences in battery capacity amount to only a few percent. However, depending on the battery size, these deviations can quickly exceed 30 Wh, which could be crucial in determining whether you make it home on a long ride. Additionally, different batteries may have the same nominal capacity but are marketed differently by manufacturers. If you’re sitting on the fence between two such bikes, this factor might wrongly influence your purchase decision.
Manufacturers are well aware of this issue and closely analyse their competitors’ specifications. To remain competitive, they often feel compelled to adjust or even enhance their own capacity figures. Each manufacturer must decide whether to play this game to survive in the tough current market. This is one reason why many manufacturers are frustrated by inconsistent capacity claims. A noteworthy example is Bosch, which has taken the lead by specifying the nominal capacity of their new batteries – 600 Wh and 800 Wh – which wasn’t the case with their older models. Bike manufacturers like MERIDA have also indicated that they plan to align more closely with nominal capacity standards in the future.
Of course, nominal battery capacity is just one piece of the puzzle, and many other factors influence the “usable capacity” of a battery pack. One crucial factor is the quality of the cells – a detail that’s often hard for customers to evaluate or even understand. Two battery packs may have the same nominal capacity but use different-quality cells. High-quality cells have a higher maximum discharge depth, meaning that they provide more usable capacity to power the motor. In contrast, cheaper cells may not support deep discharges and require a higher remaining voltage, meaning less usable capacity and a smaller range. Additionally, manufacturers differ in how much capacity they reserve for functions like lights, displays, and electronic shifting. This also affects the amount of energy available for propulsion.
What do manufacturers say about the battery confusion?
Needless to say, we asked all the manufacturers listed in the table above for a statement. Not all of them reached out for a comment, but we’ll update the article should we receive additional responses.
Our claimed capacity is sometimes higher than the nominal capacity because the rated capacity is measured under standardised test conditions, which often differ from real-world usage. For our claimed capacity, we follow the capacity specifications provided by cell manufacturers: for example, our 600Wh battery contains 30 cells, each with a Watt-hour rating of 20 Wh. Deviations from the nominal capacity mainly result from tests conducted under worst-case conditions, commonly used for determining the rated capacity. Ensuring that the measured nominal capacity aligns with the claimed capacity is a central priority for us. Transparent and reliable specifications are crucial for building customer trust. Therefore, we work closely with our battery partners to meet these standards together. Our new Bosch PT600 and PT800 batteries already comply with this approach. Likewise, our new Shimano batteries for MY26 will have a nominal capacity that exactly matches the claimed capacity. Benjamin Diemer – CEO MERIDA R&D
As one of the world’s leading technology companies, DJI is committed to providing best-in-class innovation and the DJI Avinox Drive System is no exception. When it comes to batteries, actual battery capacity depends on several factors such as the real use scenarios of the battery and also the temperature. To define a battery’s core capacity, the charging voltage, current and temperature need to be taken into consideration. A new battery is typically charged to 4.2V using a 0.2C current at 25°C, followed by discharging to 2.5V. For the Avinox Drive System’s LG M58T battery, the standard battery core capacity is 20.28Wh, with a minimum capacity of 20.0Wh. We calculate the actual pack capacity, based on a 3% remaining power calculation, is 786.86Wh, which represents 98.36% of its nominal 800Wh rating. However, in real-world applications, discharge currents are typically higher than the 0.2C rate, which can result in a reduced maximum discharge capacity—often falling below 800Wh, and in some cases as low as 750Wh, depending on the discharge current. Additionally, temperature plays a significant role in discharge capacity, with lower temperatures further impacting the ability to reach nominal capacity. This variance between nominal and actual capacity, explained above, is common in battery metrics. To present more favorable performance metrics, some manufacturers may use the standard capacity as their declared value. For most applications, the LG M58T battery is rated at 800Wh, delivering reliable performance with these considerations in mind. Ferdinand Wolf – Product Experience Director DJI
Our goal is to provide maximum transparent and practical information for users. The label on Bosch eBike batteries typically includes three values. The rated capacity, specified in ampere-hours (Ah), corresponds to the minimum value defined by the IEC61960 standard that the battery must achieve. The battery voltage, specified in volts (V), remains largely constant. The energy content, specified in watt-hours (Wh), represents the typical nominal value and indicates the capacity the battery delivers in typical use. According to the IEC61960 standard, cell manufacturers are required to specify the minimum capacity (Ah) of their cells. Despite consistent quality and performance, this value can vary slightly between cells from different manufacturers. The minimum value is used to calculate the nominal capacity at the battery level. In practice, however, the energy specification in Wh is usually slightly higher than the calculated result based on rated capacity (Ah) and battery voltage (V). For this reason, the specifications on the batteries may differ slightly. Dr. Vikram Godbole – Senior Produktmanager Bosch eBike Systems
Cell capacity (Ah) is determined under laboratory conditions following specific test procedures. Two different capacities are calculated based on different test conditions: the rated capacity (Ah) and the typical capacity (Ah), with the latter always being slightly higher. The battery pack capacity (Ah) value is obtained by multiplying the cell capacity by the pack configuration (the number of parallel branches). For all future SBC battery models, rated and typical capacity, as well as the corresponding energy in Wh (capacity multiplied by the nominal voltage), will be written on the battery label for maximum transparency. More attentive riders may realize that these values are not obtained when discharging the battery to 0%, according to the display. This is because a small portion of the capacity is reserved. This reserved capacity ensures the optimal function of the battery management system (BMS) under all circumstances. Furthermore, it allows an uncompromised riding experience right up until 0% and then keeps the lights operational for an additional 2 hours to keep you safe at night – even when the battery is displaying empty. SBC is always optimizing this reserved capacity to deliver the biggest amount of power for rider (motor) support while ensuring the safe and smooth operation of the system. Simon Maksay – Battery Engineer Specialized Bicycle Components
5.8Ah is the maximum rated capacity for each cell. We have chosen to use the maximum capacity measurement to determine the capacity of each battery because we feel it is a constant measure. Our goal is to stick to one style of measurement so consumers are able to compare generations of our bikes to one another. Another important measure is the available charge, i.e. how much the motor can use. We spend a lot of time working in our laboratory on this number and with Rise we have been able to create a control software that is able to safely use much more of the available charge, meaning a much longer range. On the new generation of batteries, the cells we are using are 21700 5.8Ah cells, which means that every cell provides 5.8Ah of capacity. Depending on the battery we have a different amount of 10 cells packs. The 630Wh main battery for example has 3 packs, the 420Wh main battery 2 pack, and the 210Wh range extender 1 pack. To know the real capacity, we multiply the battery tension (36V) by the number of cell packs (3, 2, or 1) and by the cell capacity (5.8Ah). This way we know the real capacity of the battery. Markel Uriarte – Global MTB Product Manager ORBEA
Conclusions about actual battery capacities
There are many reasonable explanations for how battery capacity is determined for marketing purposes. However, as long as so many different approaches are used, comparing battery capacities directly is unfair and, quite frankly, pointless. Therefore, we need a firmly established and transparent method that all relevant battery manufacturers follow. The method of calculating nominal capacity appears to be the most practical solution at this stage. The efforts of many manufacturers to implement and use it as a reference value already show that it’s gradually becoming an industry standard.
In our future tests, we will also mention these specifications to help promote this standard. If you want to learn more about e-bike motor systems and related terminology, be sure to check out our detailed e-bike motor comparison test.
Did you enjoy this article? If so, we would be stoked if you decide to support us with a monthly contribution. By becoming a supporter of E-MOUNTAINBIKE, you will help secure a sustainable future for high-quality cycling journalism. Click here to learn more.
Words: Peter Walker Photos: Diverse
