Can I Add A Second Battery To My E-Bike?

The bigger your battery, the longer you can ride your e-bike. These days, more and more bikes are being sold with bigger and often with multiple batteries by default, but you’re not limited to the battery your bike comes with. Most e-bike manufacturers and many aftermarket accessory suppliers offer huge batteries that you can use to boost the range of your bike considerably.

You can add a second battery to your e-bike as the controller can draw power even from a set of multiple batteries. To add a secondary battery you should a Connector. This device balances the load across batteries and thus prevents them from discharging into one another causing an electrical fire. 

This option offers an impressive set of advantages over the normal single-battery operation, including boosts in efficiency, consistency, and power output. With all of the benefits offered by two batteries, it’s tempting to try to modify your bike to take advantage of this technique. But can you add a second battery to your e-bike? Is it safe? How much will it cost? Let’s go over some of the problems.

Can I Add A Second Battery To My E-Bike?

Adding a second battery to your e-bike is a somewhat complex project and it can be somewhat costly too. 

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You’ll need to get at device to control and merge the output of your batteries, you’ll need adapters to plug this device into your batteries and your controllers, and you’ll need to open your bike up to actually plug everything in. Once this is done, you’ll need to figure out where to put the wires, the adapter, and the spare battery.

Most bikes have plenty of room on the outside to tack on some wires and a box, but your solution probably won’t look pretty. 

Even if you can access the inside of your bike’s tubes to run cable, there’s a good chance your aftermarket cables and adapters won’t easily fit through the small holes used by normal bike cables. This means that you’ll probably have a bunch of extra wiring and a small box zip-tied to the outside of your frame at the end of your project.

How Much Does It Cost To Add A Second Battery To My E-bike?

Same capacity batteriesDifferent Capcitity Batteries
Connector$60$150 – $620
Battery$50 – $750$50 -$750
Cables and adapters$10 – $40$10 – $40
Battery mount$5 – $70$5 – $70
Total$125 – $850$215 – $1,480

As you can see in this table the cost of adding a new second battery (a third one even more so) varies a lot between $125 and $1,480. If you are on the higher end of this spectrum you might even consider getting a new electric bike.

Devices that combine the output of two e-bike batteries are still somewhat new on the market. At the time of writing this page, there are two styles of device designed to combine the output of two batteries. 

One runs about $60 and requires the use of two batteries of identical nominal output voltage. The batteries can be of any capacity, however, giving you some freedom in terms of which two batteries you choose to use. 

Bolton E-Bikes’ Dual Battery Parallel Connector is a great example of this type of device. In addition to the $60 for the connector itself, expect to spend at least $40 on cables and adapters.

The second style of device works with batteries of differing voltages and costs $170 or so. The Datex2 or Date Dx are good examples of this type of connector. 

These more advanced devices can even allow you to charge both batteries at once through the connector, although this will require a certain type of battery and may increase the cost of the connector. Just like with the first type of connector, expect to spend at least $40 on cables and adapters.

Income School

In addition to the device needed to run two batteries in tandem, you’ll need to purchase a second battery and a set of hardware to mount both the battery, the extra cables, and your battery connector on your bike. 

If you’re just throwing a spare second battery in a bag that already lives on your rear rack, you can probably get away with buying a bag of zip ties and not much else. 

If you need to purchase a high-capacity battery and you’d like a mounting solution that looks like it came from the manufacturer, you’ll need to spend a lot more. 

Batteries vary greatly in cost based on manufacturer, capacity, voltage, and form factor. Depending on your needs, you might spend between $50 and $750 on the second battery alone.

Why Do I Need A Special Device To Connect Two Batteries To My E-Bike?

Lithium batteries are complicated bits of technology that can be very dangerous when used incorrectly. Plugging two batteries into the same circuit is very much an incorrect use. When two batteries live on the same electrical path, they’ll try to share charge levels with each other. 

If the batteries are very close to each other in voltage and charge, will just result in the batteries powering everything else on the circuit in tandem. 

If they’re not at the same charge level and voltage, however, they’ll try to instantly equalize their charge levels to bring everything into balance. In other words, if you put a battery at 100% charge and a battery at 50% charge on the same circuit, the 50% charge battery will try to siphon 25% charge off of the fully charged battery over the course of a few seconds. This is bad. 

At best, you’ll fry the BMS on one or both batteries and one of the batteries will remove itself from the circuit. At worst, you’ll start an electrical fire. Fires involving lithium batteries are notoriously difficult to put out, meaning this is NOT something that you should attempt to mess around with in your garage. 

Stick to using battery connectors from reputable sources and follow the directions given by the manufacturer to minimize the risk of causing this dangerous situation by accident.

Devices designed to run two batteries in parallel dodge this problem with a bit of clever engineering. Instead of allowing both batteries to connect to the circuit at the same time, the devices check the voltage levels of the batteries and only let the battery with the highest voltage (and therefore charge) power your bike. 

When that battery eventually reaches the voltage level of the second battery, both batteries will be brought onto the circuit in tandem. With identical voltages and charge levels, the batteries won’t send huge amounts of power to each other and will instead power your bike’s motor safely.

Sam Benkoczy

Hi, I'm Sam. I own and maintain 6 e-bikes, 15 regular bikes (road bikes, folding bikes, hybrid bikes, city bikes among others). I learned about bikes from my local bike mechanic as well as from bike maintenance courses. I love being out there in the saddle, and using my bike as a practical means of transportation. You can also find me on my YouTube channel at Say hi to me at

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