It is not uncommon for e-bike owners to come up with the idea of installing a 2nd battery pack. Most often, such a desire arises after buying a budget e-bike with an insufficiently capacious battery.
Sometimes a sufficiently large battery capacity is not enough, especially when traveling in difficult conditions or over long distances.
Therefore, an additional battery on an e-bike is most often installed by riders who are fond of cycling, downhill, riding on rough or mountainous terrain.
In such cases, a dilemma arises: to replace the used battery with a more capacious model or to use another battery in addition to it.
If the characteristics of the energy storage device used have decreased due to “old age” and natural wear and tear, it will be optimal to replace it.
If the battery is working properly and has not yet worked out even half of its resources, but its capacitive characteristics do not suit you, you should think about installing an additional battery.
How Are 2 Batteries Connected?
Before you connect two batteries to an electric bike, you need to choose the best option for connecting and using them.
To increase the total capacity, the batteries are connected in parallel – plus to plus, minus to minus.
The voltage of the connected blocks must be the same, and with a parallel connection, its value does not change. For example, when connecting 2 batteries with a voltage of 48 V and a capacity of 36 Ah, we get a common power supply for 48 V and 72 Ah.
This connection option is considered optimal (compared to alternate use), because provides batteries with milder operating conditions, without high current loads. The discharge current is distributed to 2 batteries, so the load on each of them is reduced.
In fact, some energy storage devices are used as 1 large assembly.
But the characteristics of the batteries connected in parallel must be identical:
- The same chemical composition (in tandem with the Li-ion block we use Li-ion, with LiFePO4 – LiFePO4);
- Equal voltage.
The capacity may vary and is selected taking into account the required increase in range. For safe operation, each battery pack has its own BMS board. The accumulated electricity in this case is evenly consumed in both assemblies.
Before charging, the battery packs are separated, and each of them is connected to its own charger. Before the next connection to the electric motor, it is important to check the voltage on both batteries so that it matches, and only then connect them.
Consistently
If you apply a serial connection (minus to plus), the capacitance of the assembly will not change, and the voltage will be summed up. Such a need may arise when installing a new, more powerful motor with increased voltage.
For example, when replacing an electric motor with a rated voltage of 24 V with a 48 volt battery, 2 24 V batteries can be connected in series. In practice, such cases are rare.
Usually, the installation of a new motor is accompanied by a complete replacement of the energy storage device.
Alternate Application, No Connection
In addition to parallel and series connection, the option of independent, alternate use of 2 batteries is possible. For example, you can assemble 2 independent circuits and power 2 motor wheels from them.
This method is relevant for all-wheel drive electric bicycles.
If there is only one motor, you can connect the battery to it one by one, by switching with a switch. Sometimes cyclists carry a spare battery in a backpack or bag and, when needed, install it in place of a dead drive.
Compared to a parallel connection, the current loads when the battery packs are connected in series will be higher. As a result, battery life will be reduced, especially when powered by powerful electric motors.
But it is not necessary to strictly observe the identity of the batteries used – for example, you can alternately use the Li-ion and LiFePO4 model, the old and the new battery.
Where To Install An Additional Battery?
Mounting of the 2nd battery pack can be done in the frame space, on the trunk, seatpost, and steering rack.
A suitable location is selected according to several criteria:
- The presence of free space that is not planned to be used to install other devices and accessories;
- Rider preferences and comfort;
- Correct weight distribution, even distribution of the load on the electric bike;
- Protection of batteries from possible damage.
To protect against external factors, instead of battery bags, it is better to use hard shock-resistant cases with a high degree of dust and moisture protection.
How To Connect?
For parallel connection, you need to add a connector for the 1st battery, organize an extension cable for the 2nd battery, install it in the chosen place and connect it correctly: positive terminals – in one terminal, negative – in the other.
Both energy storage devices must be in good condition. If you use a new battery in parallel with a worn-out power source, they will both fail faster.
When connecting an additional battery, it is important to take into account the increased load on the wiring through which electricity is transmitted, and use reinforced wires.
To make the battery circuit more efficient, it is advisable to install both batteries close to each other and connect them with short wires. If the wires are long, the extra resistance will result in energy loss.