LEAD-ACID ELECTRIC BIKE BATTERIES (SLA)
Lead-acid electric bike batteries are cheap and easy to recycle. However, they are sensitive to bad treatment, and they don’t last very long. They are not a good choice if you’re serious about actually using your bike to commute.
Lead-acid batteries are cheap for several reasons: they weigh twice as much as NiMh batteries, and three times as much as lithium batteries. They have much less usable capacity than NiMh batteries or lithium batteries. They only last for half as long as nickel or lithium batteries.
Warning: if a cheap electric bike is advertised and the advert does not state what kind of battery it has, you can pretty much be certain that it has a lead-acid battery. It might be cheap, but it’s not a bargain. This battery type might be good enough if you want the bike as a mere toy, to be taken out and played with occasionally in your immediate neighborhood – but if not, it would be better to avoid these batteries altogether.
NICKEL-CADMIUM (NICD) ELECTRIC BIKE BATTERIES
Weight for weight, nickel-cadmium (NiCd) batteries have more capacity than lead-acid battery, and capacity is an important consideration on an electric bike. However, nickel- cadmium is expensive and cadmium is a nasty pollutant and hard to recycle. On the other hand, NiCd batteries will last longer than lead-acid batteries. But the reality is that because they are so hard to recycle or get rid of safely, NiCd batteries are rapidly becoming a thing of the past. These are also not a good choice of battery type, regardless of price.
NICKEL-METAL HYDRIDE (NIMH) ELECTRIC BIKE BATTERIES
NiMh batteries are somewhat more efficient than NiCd batteries, but they are also more expensive. Most people’s report that NiMh offers little improvement in range over NiCd. On the other hand, they will last longer and are easier to dispose of correctly. Nonetheless, NiMH batteries are also becoming a rarity, because the market place is being taken over by Lithium-ion (Li-ion) batteries.
LITHIUM-ION (LI-ION) ELECTRIC BIKE BATTERIES
These have become the default battery, capturing over 90% of the market. But to complicate matters, there are many different kinds of Li-ion batteries. On the plus side, Li-ion batteries last longer and generate more power for their weight than other batteries. On the negative side, they are fussy little creatures, and require a genius-inspired smorgasbord of electronic features to prevent them from self-destruction and even catching fire! Of course, none of those are your problems, as the manufacturer will have sorted out the genius side. But like all good things in life, this comes at a price: this battery type is very expensive, and shows little sign of getting cheaper.
LITHIUM-ION POLYMER (LI-POL) ELECTRIC BIKE BATTERIES
This is a new one, and promises to be no better than the Li-ion battery type in terms of range, weight, or price. However, it can be molded into interesting shapes. They contain no liquid, so they don’t require the heavy protective cases that other batteries need. Also, this absence of free liquid theoretically means that they should be more stable and less vulnerable to problems caused by overcharge, damage or abuse. In general, they seem to be ideal for use in high capacity, low power applications – such as electric bikes.
Given the new trend to make electric bikes look just like other bikes, I am guessing that some creative manufacturers will come up with some radically cool ideas. I wouldn’t rush into buying one of these battery types, however, until they prove themselves in terms of battery life.
LITHIUM COBALT (LCO) ELECTRIC BIKE BATTERIES
This is another variation on Li-ion. It’s a relatively new kid on the block, and its proponents claim it has much higher energy density than other lithium batteries, so that it offers optimum power in a light, compact package. For example it is used in Optibikes, and the manufacturers claim “no other electric bike can go as far as an Optibike, guaranteed”.Yet another one that still has to prove itself, though.
LITHIUM MANGANESE (LIMG204) ELECTRIC BIKE BATTERIES
This is another new kid on the block, and is the same battery technology used in the Nissan Leaf hybrid car. Some claim it is the best of all. For example it is used in Elite Electric Bikes, and the manufacturers claim that it lasts longer and generates more power than other Lithium batteries.
WRAPPING UP THE ELECTRIC BIKE BATTERIES DEBATE
As you can see, it is hard to know whose claims to believe. It does seem however that lithium cobalt offers higher energy density, but that lithium manganese batteries are somewhat safer, and are more environmentally friendly. This comes from an unbiased source:
“Lithium Manganese provides a higher cell voltage than Cobalt based chemistries at 3.8 to 4Volts but the energy density is about 20% less. It also provides additional benefits to Lithium-ion chemistry, including lower cost and higher temperature performance. This chemistry is more stable than Lithium Cobalt technology and thus inherently safer but the trade off is lower potential energy densities. Lithium Manganese cells are also widely available but they are not yet as common as Lithium Cobalt cells. Manganese, unlike Cobalt, is a safe and more environmentally benign cathode material. Manganese is also much cheaper than Cobalt, and is more abundant.”
In sum, the best choice is some kind of lithium ion battery, but the jury is still out on which is the best lithium ion battery. If the electric bike you are considering comes with any kind of lithium ion battery, you are off to a good start. Beyond that, you need to weigh up what is more important to you:
- proven safety and range (Li-ion);
- higher energy density (LCO);
- performance coupled with safety, but relatively new (LiMg204); or
- cool shapes and cutting edge (Li-pol).
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