Ebike Batteries

The race is on to develop the ultimate battery with individuals and large companies all over the world competing to build a cost effective, environmentally friendly, light weight battery with high energy density that is quick to charge. There will most likely be large royalties for the people who come up with the best technology. Nearly all of the gadgets we have these days are reliant in light powerful batteries. Phones, electric cars (which we will see more of over the next decade), cameras, ebikes and many more things. With this increasing demand we will see rapid development in battery technology.

There are a lot of different chemical makeups for batteries but probably only about 3 types are currently manufactured that are suitable for electric bikes. Lead Acid(PbA),  Nickel Metal Hydride (NiMH), and Lithium-ion or Lithium Polymer.

Sealed Lead Acid  for ebikes – SLA

Lead-acid Batteries were one of the original forms of battery to be developed over 100 years ago. They are a tried and proven technology and they are cheap, but they are heavy. The newer sealed lead acid batteries are virtually maintenance free and are cheap to produce compared to a lot of the newer technology. These have been widely used in many ebikes but they have some major short comings, too heavy, charge time too long and if they are run too low too often it can ruin them. With the price of some of the more high-tech batteries coming down I think Lead acid batteries will be phased out of the ebike world. But for now they can be a cost effective way to get rolling with an ebike.

• Specific energy:     30–40 Wh/kg
• Energy density:     60–75 Wh/l
• Specific power:     180 W/kg
• Charge/discharge efficiency:     50%–92%
• Energy/consumer-price:     7 -18  Wh/US$
• Self-discharge rate:     3–20%/month
• Cycle durability:     500–800 cycles
• Nominal cell voltage:     2.105 V

* sorced from Wikipedia

Nickel Cadmium Batteries for ebikes – NiCad

Nickle Cadmium Batteries have similar performance to the Nickle Metal Hydride Batteries (below) but have pretty much been super seeded now. The Cadmium is a fairly toxic heavy metal which is difficult to dispose of and there are many countries around the world trying to phase them out.

• Specific energy     40–60 Wh/kg
• Energy density     50–150 Wh/L
• Specific power     150 W/kg
• Charge/discharge efficiency     70–90%
• Self-discharge rate     10%/month
• Cycle durability     2,000 cycles
• Nominal cell voltage     1.2 V

Nickel Metal Hydride Batteries for ebikes – NiMH

NiMH batteries are fairly fast to charge they are lighter and less toxic than lead acid batteries and have a much higher energy density, close to Lithium batteries. They have been enjoying some popularity in ebikes but it looks like the newer lithium batteries are out selling the NiMH batteries.

NiMH batteries have a few significant short comings. They have a very large discharge rate when not being used, loosing up to 20% of their capacity in the first day. Performance is reduced in cold weather and they need to be fully discharged at regular intervals to maximize battery life.  So they do perform better that SLA batteries but are still not perfect.

• Specific energy     60–120 Wh/kg[1]
• Energy density     140–300 Wh/L
• Specific power     250–1000 W/kg
• Charge/discharge efficiency     66%
• Energy/consumer-price     2.75 Wh/US$
• Self-discharge rate     30%/month (temperature dependent)
• Cycle durability     500–1,000
• Nominal cell voltage     1.2 V

eBike Batteries Lithium Ion – Li-ion

Lithium-Ion batteries are light and maintenance free. They last a long time and can be quickly charged. The chemistry in them is complex and they are fairly unstable so the need to have a battery management system built into them to ensure they don’t over charge or melt down. These batteries have been super seeded by the LiFePO4 batteries. So it is probably better to not bother with them.

Lithium Polymer Batteries – LiFePo4

The Lithium Polymer battery is probably one of the top styles of batteries for electric bikes at the moment. It is light, holds lots of power, and is maintenance free. The better brands are claiming 2000 cycles without significant degrade in performance. It can also be drained completely or partly with out damaging it. Where as Lead Acid batteries will be degraded if they are run completely flat too often. Or NiMH will be degraded if they are not drained regularly. If you want excellent power to weight and no maintenance these are the batteries to choose.

Price is most often the deciding factor when choosing your batteries as they are often the most expensive part of an electric bike conversion. Lead acid batteries are the cheapest going up to Lithium Polymer batteries. Currently you will be looking at between $150 to $600 for a battery.

Specific energy     90–110 Wh/kg
Energy density     220 Wh/L (790 kJ/L)
Specific power     >300 W/kg
Energy/consumer-price     0.5-2.5 Wh/US$
Time durability     >10 years
Cycle durability     2,000 cycles
Nominal cell voltage     3.3 V

Comparison Table for Common Batteries