Batteries are at the heart of a lot of what we do in our lives. From the way that we need to charge our phones (often with frustrating regularity) to a watch being able to run for years on a tiny silver disc. Each do the same basic thing, but the difference in them is huge.
As the industry has matured and the number of e bikes has increased, the development of these batteries has increased, and it's all down to the rise of the Lithium Ion battery.
In the same way that LEDs quickly became the only option for bike lights, Lithium Ion is now completely dominant in bike batteries. It's the same technology you’ll find everywhere from your phone and electric drill to a Tesla supercar. They are smaller and lighter than the lead acid batteries they replace, meaning lighter bikes and more range for less weight, and the reduced environmental and safety risks make them far more suited to consumer use.
Lithium Ion batteries last much longer than lead acid batteries. Typically a lead acid battery needs to be replaced after 200-300 charges, whilst a Lithium Ion battery is likely to last between 500-2000 charges, depending on battery quality, and that's only set to increase with new batteries claiming a service life of up to 12 years. Charging is also a lot more efficient, with a fast charger able to fill up an e-bike battery in just a few hours. The only major downside to Lithium Ion batteries is that the charging process needs to be more carefully regulated to avoid damaging the cells, and that adds a little bit to the overall cost. Normally the electronics needed to control the charge are added into the the battery unit.
Lithium polymer batteries are a subset of Lithium ion; the battery functions in a similar way but the process uses a non-rigid container instead of grouping separate solid cells together. This allows battery manufacturers to create a greater variety of battery shapes, with a lighter construction. Lithium polymer batteries are mainly used for smaller devices (your phone will contain one) but some electric car manufacturers have used them in vehicles, and the ability to customise the shape of the battery is a bonus in e-bikes where manufacturers are integrating the batteries into the shape of the frame.
Capacity is usually measured in Amp hours (Ah) or Watt hours (Wh). They're both essentially measuring the same thing but Watt hours is taking over as the standard because it's a bit more consumer-friendly.
The relationship is simple to explain: a battery with a 10Ah capacity is theoretically capable of supplying 1 ampere of current for 10 hours (or 10 amperes for 1 hour). Multiply that by the voltage the battery supplies – in e-bikes this is usually 36v, although 24v and 48v systems are also available – and you get the capacity in watt-hours, since power – measured in watts – is simply the voltage multiplied by the current. So a 10Ah, 36V battery is 360 Watt hours (Wh).
e-bike batteries have a range of capacities. The battery is usually the most expensive part of the bike to produce, so cheaper bikes tend to have smaller batteries. The cheapest bikes have batteries of around 150-200Wh, with 300-500Wh the standard range. Bigger batteries are available, with some manufacturers (such as Koga) offering batteries with a capacity of over 600Wh, and Ariel Rider debuting a 900Wh battery at Eurobike this year.
It used to be the case that Lithium Ion batteries were very expensive. But like any emerging technology, developments in the tech and economies of scale mean that the price of batteries has dropped massively, and will continue to do so. Back in 2005 it cost about $1,000 to make a Lithium Ion battery with a capacity of 1,000Wh. Ten years later, the cost had dropped to just $250. And that trend is set to continue, because the world supply of Lithium Ion batteries will be ramping up massively in the next few years.
Part of this is down to Tesla, the motor company. Actually, they see themselves as more of a battery company, offering not only electric cars but also home battery storage. They're building an enormous facility, the Gigafactory, which on its own will produce 35 gigawatt hours of batteries every year. That's enough for about 70 million e-bikes.
If everything else stayed the same that single factory would, on its own, more than double the world production of batteries which currently stands at about 30GWh. But others are following suit: two of the biggest Chinese battery manufacturers plan to be producing 60GWh of batteries between them by 2020. So in the next four years world battery production is set to quadruple, and for e-bike customers that's going to mean much lower prices.
Another key reason why Lithium Ion batteries have become more popular amongst the European and US markets is their ease of disposal and recyclability compared to lead acid batteries.
In several states in the US and in the EU it is illegal to dispose of lead acid batteries, so getting rid of them once they have come to the end of their functional lives is difficult.
Lithium Ion, on the other hand, has less environmental impact as a technology, and fewer regulations, meaning that the batteries can be both disposed of and recycled more easily. The recycling process is actually slightly more complex, despite the lack of regulations, but with the rise in number of this battery type, it will be streamlined in the future. By 2020 there will be an estimated 5GWh of used batteries coming into the market from the first generation of electric cars, many of which will be repurposed into the growing home storage market: used batteries still have reasonable capacity, and for static operations there's less need for them to be small and light. Others will be recycled, adding to the overall world production capacity.