Electric bike batteries, and battery charging issues
As the power source, the battery is a critical component of your electric bike and an important criteria in your purchase choice.
Types of batteries
Electric bike manufacturers are moving toward lithium ion (Li-Ion) batteries these days, as these are light, compact and pack more power in a smaller space than other battery types.
Common alternatives are NiMH batteries and the lead-acid battery you typically find in cars. Lead-acid batteries in particular are disappearing fast, though. They are cheap, but are also simply too heavy, slow to charge and have a relatively short lifespan.
A battery's power is reflected in Watt hours. The bigger the number, the greater the potential power boost and likely range of the battery. A decent battery should give you at least 15 miles of cycling.
The given Watt number may seem higher than the maximum motor power allowed under law, but this is misleading.
First, the power gets diluted as it's converted through the motor and components into actual work applied to the bike.
Second, the battery output typically refers to the maximum power output, but not the continuous power input (which is what the law worries about). You would typically want the battery/motor to provide a boost of 100-200W under normal conditions, with a maximum power output of anything up to 600W, depending on how much of the short-term lifting work you want it to do on the hills.
Most manufacturers will specify the typical distance you can get out of a bike's battery. However, although battery performance is important in determining this distance, there are many other factors involved. For example:
- the faster you go and the more you draw on help from the motor, the shorter the range
- road conditions: headwinds, hills and slow surfaces (think mud!) drain the battery faster
- weight: the more the bike has to pull or carry, the shorter the range
- bike condition: dirty components and flat tyres limit how far you can go
Even the performance of the battery itself depends on its age, temperature etc.
As such, it's important not to take stated battery ranges as guarantees, and build in a good reserve when planning journeys. Not least because electric bikes are heavier than your normal bike. So it's harder work if you're reduced to pedal power only!
Battery maintenance, charging and lifespan
The cost of recharging the battery is normally negligible: a few pence per charge.
Charging times themselves vary considerably, depending on the type of battery and the efficiency of your charger, but rarely exceed 6 hours in modern batteries. Most bike owners tend to leave the battery to recharge overnight. You may also be able to purchase express chargers.
Battery life is prolonged by not allowing it to discharge fully before recharging: keep it topped up as much as possible. Check the instructions, though. NiMH batteries, for example, typically need to be run down to empty around once every three months.
Experts commonly recommend recharging before the capacity is down to about 50% of full. As a result, consider the distance travelled on your typical daily journeys and double the number when deciding how much battery power you need in your bicycle.