Adding a dual battery to your electric bike. Bosch ebike range extender

Adding a dual battery to your electric bike

What’s better than a big battery on your electric bike? How about two big batteries? The latest innovation in electric bikes is a nifty technique to give you lots of extra range without requiring that you carry all that battery with you all of the time. By adding a secondary battery pack that works in tandem with your main battery, you get the benefits of an extremely large battery but the flexibility of smaller batteries that you can hot swap on or off the bike.

Bosch Dual Battery

The company that first pioneered dual battery options was Bosch. For years now they have offered a dual battery splitting cable that allowed manufacturers to add secondary batteries, allowing for better designs and more range.

In recent years some manufacturers have offered after-market dual battery kits that can be installed by a dealer. Bikes from Gazelle, Orbea, Benno, Tern and Riese Müller all offer integrated dual batteries or after-market dual battery kits. If your bike does not include a dual battery, we can install a secondary battery harness. Cost ranges based on the bike but installation typically takes around an hour and a half and the parts themselves cost around 1000 including the battery.

Range Extenders

Another more recent innovation from Specialized and Orbea is the concept of Range Extenders. Range extender systems augment oftentimes a smaller main battery to offer amazing range while keeping the overall bike extremely low weight. Range extenders are typically smaller than the dual batteries offered from Bosch (around 350wh versus 500wh for Bosch) but are defined by their sleek profile and low weight.


Get in touch to learn more about the latest bikes that feature extra battery capacity or to find out if your bike can be upgraded with a dual battery system.


Limitless riding enjoyment: Whether you’re taking a jaunt through the countryside or cruising through the city – using the PowerPack or PowerTube means there’s no limit to riding enjoyment. There’s a suitable rechargeable battery for every requirement and every type of eBike; whether it’s the rack variant, frame battery or the integrated solution. Thanks to their enormous range, long service life, intelligent battery management system and easy handling, Bosch lithium-ion batteries are among the most modern on the market, so all those decades of Bosch experience pays off!


PowerPacks are the fuel tanks of pedelecs. State-of-the-art lithium-ion technology makes them into efficient and longlasting suppliers of power. As an eBiker you can ride with them very conomically and thus maximize the range of a rechargeable battery charge.

TIRE PRESSURERolling resistance can be minimized by proper tire pressure. Tip: In order to maximize the range, inflate the tires to the maximum permissible tire pressure.

RECHARGEABLE BATTERY TEMPERATUREWith decreasing temperature, the efficiency of a rechargeable battery goes down, since the electrical resistance increases. In winter you can thus expect a reduction in the normal range.

CADENCE Cadences above 50 revolutions per minute optimize the efficiency of the drive unit. In contrast, very slow pedaling is very costly in terms of energy.

STARTING BREAKINGAs with a car, frequent starting and stopping is less economical than long distances at a nearly constant speed.

GEAR SHIFTINGCorrect shifting also makes eBiking more efficient. It is best to start off and take inclines in a low gear. You then switch to a higher gear in accordance with the terrain and speed.


The more conscientiously you treat the PowerPack, the further it will take you.

CHARGINGThe battery should be charged under dry conditions and at room temperature.

STORAGE DURING WINTERStore the batteries in a dry location at temperatures between 0 and 20 °C. Storage at room temperature is ideal. Being completely charged or completely discharged for storage is not advised for the batteries. The ideal charge status for lengthy periods of storage is approx. 30 to 60% or two to three LEDs on the battery indicator.

STORAGETemperatures below.10 °C and above 60 °C should be avoided.

adding, dual, battery, your, electric, bike

TRANSPORTFor transport, the battery should always be taken off the eBike and safely transported in your car, for example.

CLEANING CARE Cleaning with a direct water jet is impermissible, in particular to protect the electronic components. Before cleaning, remove the battery. Occasionally clean and lightly grease the plug terminals.

WINTER USEDuring winter use (particularly below 0 °C) we recommend charging and storing the battery at room temperature before inserting the battery in the eBike immediately before riding it. For frequent travel in the cold, it is advisable to use thermal protective covers.

INSPECTIONUsing a diagnostic unit, the dealer can check the health status of the eBike, especially the battery, and tell you the number of charging cycles.


The service life of a PowerPack is influenced mainly by the type and duration of use. Like every lithium-ion battery, a PowerPack also ages over time, even if you do not use it.


  • Low load
  • Storage at a temperature between 0 and 20 °C
  • Storage at approx. 30 to 60% charge statuscycles
  • Parking the eBike in the shade or a cool location


  • Heavy-duty use
  • Storage at over 30 °C ambient temperature
  • Prolonged storage in a completely charged or completely discharged state
  • Parking of the eBike in the blazing sun



The charging time depends on the capacity of the battery and the charger type. The graphics show how quickly the various batteries can be charged with a particular charger.


PowerPacks and PowerTubes are particularly easy to charge directly on the eBike itself. You just need to insert the charging plug on the charger into the charging socket in the battery mount and insert the power plug into the wall outlet. Done! The batteries should be charged at room temperature in a dry location where a smoke detector is installed.


If the battery cannot be charged directly on the eBike, the PowerPack and PowerTube can also be easily removed.


The infrastructure of charging stations for eBike batteries is now well developed in many regions. Along popular bike routes, eBikers have access to an increasingly dense network of charging stations. In order to drive this development forwards, we now have a strong partner at our side with Bike Energy. This means that breaks from riding can be used as an opportunity to charge the eBike battery, free of charge.

How to get the greatest range from your electric bike

The range that your electric bike can travel on a single charge is always a big selling point, there are even tools to make such calculations accurately. We all enjoy the freedom and reassurance of knowing there’s plenty of energy left in the tank, even if we undertake only short journeys, so it makes good sense to be clued up on the subtle power saving tips that can retain power for when you really need it.

So, what factors dictate how far you can go before running on empty? And how can you hold off that moment for as long as possible?

“Many elements influence the range of an e-bike,” says Chris Astle from drive system maker Bosch.

“These include the support mode, the drive unit model, the battery’s size, the rider’s cadence, the way they use their gears, the amount of accelerating and braking, the tyre pressure and even the rider’s body profile.”

Even ignoring factors such as temperature, wind and terrain, these reasons mean different bikes and riders can achieve drastically varying distances even on flat roads.

When Cycling Electric publishes a manufacturer’s ‘stated range’, we do so with the caveat that there are countless variables in play that will influence the true figure. A charitable person might suggest that these myriad variables are why many makers’ range estimates are often wide of the mark. A more cynical person might think exaggerated predictions in catalogues have become a marketing tool.

Calculating your potential

“We have two ways of testing the range of our bikes,” says Marco Sonderegger from bike maker Specialized. The first is by investigating the mechanical properties of each component in the drivetrain.

“First you have the electrical consumption of the engine in watts. Then you have losses.” These mechanical factors reduce the power delivered to push the rider forward. By far the largest of these is the efficiency of the motor itself.

“If you have a mid-drive motor that’s consuming 600 watts of power, and you have losses of 20%, then 480 watts are being delivered to the cranks,” explains Sonderegger.

The capacity of e-bike batteries is generally described in watt-hours (Wh). This unit of energy is equivalent to one watt of power expended for one hour.

“Take the 710Wh battery on our Turbo Vado bike,” says Sonderegger. “It means the bike will provide one hour and 11 minutes of support on full assist mode at a continuous 600 watts, with 80% of that energy going into propelling the rider.”

Of course, full gas all the time isn’t how anyone rides in real life – or how e-bikes relying on pedalling assistance are set up to work.

adding, dual, battery, your, electric, bike

Instead, to understand what these numbers mean for the average rider, Specialized also conducts extensive real-life range tests. These might see a rider on one of its mountain bikes linked to a GPS sent over a couple of mountains while technicians measure everything from gradient and cadence to air temperature.

From this data, Specialized can put a number on the range of each of its bikes. However, because of the way usage varies, you’ll find the capacity of its e-MTBs are rated in hours, while its active line bikes come with a range quoted in miles.

“We use hours on the mountain bikes because most people will be using the bikes to climb mountains,” says Sonderegger. “And when you’re climbing mountains, your range in miles can look like nothing. Some people will see the quoted range and think they can ride that uphill. But most brands’ quoted ranges will be on absolutely flat terrain and with no stops.”

What to look for

Of course, how companies decide what constitutes “normal use” and therefore the range they suggest you might achieve remains up to them. You’ll also find even the most honest brands take a pretty optimistic approach to how much energy the average rider might want to contribute. This left us wondering: might battery capacity be a better indication of a bike’s likely range?

“Knowing the battery’s capacity is only useful if you know how much energy your motor consumes,” says Sonderegger.

“It’s like fuel consumption on a car. The battery is the tank. When driving, you want to know your fuel per mile. On a bike, you need to know your watt-hours per mile.”

Like a fuel-efficient car, a bike with a more efficient electric motor makes the most of the energy stored in the battery and takes you further before needing to be replenished.

Efficiency between different e-bike motors varies hugely, however.

“If we ignore less efficient hub-drive systems and just consider mid-drives, the difference can still be as much as 30%,” says Sonderegger. This variation means you could attach the same battery to two superficially similar bicycles and achieve vastly different outcomes.

Clearly, both battery capacity and motor efficiency are vital in determining how far your e-bike will go.

Maximising your ride

Drive system maker Bosch has recently developed a range calculator tool to help riders better understand how their electric bike might perform. You input a range of data and it calculates the distance you’ll achieve. It’s a great way of seeing what effect different factors have on performance. It’s also interesting to see that even among the firm’s own products, switching models can vary your potential range by over 10km.

But assuming you’ve already got an e-bike, how do you maximise the range you can achieve?

If you’re using a mid-drive motor, it turns out that how quickly you pedal, and not just how much effort you put in, has a significant effect. This is because mid-drive motors have a rotational speed at which they work best. This is dictated by how fast you turn the pedals. It’s a bit like the revs on a car.

“Cadences above 50rpm will optimise most drive units’ efficiency,” says Astle. “Very slow pedalling is costly in terms of energy.” This efficient cadence range is dictated by the internal gearing hidden within the mid-drive.

By contrast, hub-based motors work best at speeds dictated by the diameter of the wheel into which they’re built. This means you’ll need to target a particular velocity rather than the rate at which you rotate the cranks to get the best results. The inability of hub motors to tailor themselves to the speed at which the rider is pedalling is one big reason why they’re inherently less efficient than mid-drives.

Nevertheless, whichever style of motor your bike employs, correctly using your gears rather than simply letting the motor make up the difference will also help. “Correct shifting, where you start off and take inclines in an easy gear, then shift to a higher one following the terrain and speed, makes a big difference,” says Astle.

Of course, you can always elect to provide more power yourself. “Changing the ride mode to provide less support will increase the range,” says Astle. “But you’ll need to exert more effort.”

It seems that, like everything in life, when it comes to maximising the range of your e-bike, what you get out is dictated by what you put in.

In summary, what are the quick wins to get the peak range from your electric bike?

Finally, have a read of our explainer on charging your battery. There are best practice tips for prolonging its life and thus your range too.

Trek unveils two kid-carrying electric cargo bikes, and they sure look familiar

Wisconsin-based bicycle maker Trek has just launched its latest two electric bikes, which are both designed as kid and cargo movers. The new Trek Fetch Plus 2 and Trek Fetch Plus 4 mark Trek’s deepest dive into the cargo e-bike segment yet.

Family-friendly cargo e-bikes

The two e-bikes carry distinct designs, with the Trek Fetch Plus 2 rolling out as a longtail cargo bike and the Trek Fetch Plus 4 taking on less common front loader cargo bike layout.

Long tail cargo bikes have a stretched wheel base with extra space between the rider and rear wheel. Front loader cargo bikes, sometimes referred to by their Dutch name bakfiets, have a long platform or box in a stretched space between the rider and front wheel.

Both categories are becoming increasingly common and we’ve seen dozens of examples from various companies in the past couple years.

But this time it’s Trek that is hankering for a slice of the cargo e-bike pie as the company puts it’s own spin on the two popular e-bike categories.

Trek Fetch Plus 2

The Trek Fetch Plus 2 will use Bosch’s BES3 Smart system with the company’s cargo-specific mid-drive motor lineup. Those motors are rated for a continuous 250W of power, though their 80 Nm torque rating betrays the true higher power of the drive system.

The motors are usually limited to 20 mph (32 km/h) in the US, and the throttle-less design keeps them squarely in the Class 1 e-bike designation.

The Fetch Plus 2 includes Bosch’s 500Wh battery that mounts in the downtube and is removable for charging. That battery is a bit below average capacity for e-bikes in the US, but should still offer plenty of range thanks to the efficient pedal-assist setup of the Bosch drive system. An optional range extender battery will be available for those that want to carry more than 500Wh of battery with them.

The bike is rated for a combined operator-and-passenger payload capacity of 200 kg (440 lb). That puts it in competition with other heavy-hauling electric cargo bikes like the Tern GSD, though it carries a higher entry price.

The Fetch Plus 2 will go on sale in April of this year with an MSRP of US 5,999.

Trek Fetch Plus 4

If you thought the Fetch Plus 2 was pricey, wait until you check out the 8,999 Fetch Plus 4.

The bike uses a similar drivetrain but swaps in a 750 Wh battery. That higher capacity battery is better suited to the heavier Fetch Plus 4, especially considering the obvious kid-carrying front bucket will likely be occupied much of the time.

That’s a big part of the draw, as Trek’s designer Eric Bybee explained:

Kids were the center point of when we first started designing these. We realized that when a family is going out to buy one of these bikes, the kids have to be the FOCUS.

The Fetch Plus 4 includes a high-end transmission using a Gates Carbon Drive belt-drive system paired with an automatic shifting Enviolo hub in the rear wheel. That’s a fairly significant upgrade over the Fetch Plus 2’s 10-speed Shimano Deore transmission, though even that chain drive setup is nicer than we see on many other cargo e-bikes. Both models carry four-piston hydraulic disc brakes – another nod towards their heavy weight ratings.

While the Fetch Plus 2 looks similar to several other longtail cargo e-bikes we’ve tested before, the Fetch Plus 4 draws from a more European vibe seen in higher end cargo e-bikes like those from Urban Arrow, Riese and Müller, and others.

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