Choosing an Electric Bike Battery

Advice on Buying Rechargeable Electric Bicycle Batteries

Jul 17, 2009
Helen Smeaton

Sealed Lead Acid Battery for an Electric Bike - E-Bikekit.com

Choice of electric bike battery will affect bike weight, riding distance, recharging time and battery life. Here's some advice on choosing one.

E-bikes are becoming more popular as a green and healthy means of virtually sweat-free transport. Whilst popular in Asia they are still something of a niche market in Europe and the US partly due to battery weight and the inconvenience of recharging times.

With worldwide emphasis on finding more eco-friendly methods of transport however, the spotlight is back on battery-powered methods of transport so technological advances are filtering their way through the to e-bike market.

How Electric Bikes Work

Motorized bicycles offer power-assisted cycling, the motor being powered by a rechargeable battery. The cyclist still has to do some work especially when starting off and also on hills although the strain of hard pedaling is taken off the rider by using the motor. Lazy riders can opt to let the motor do nearly all the work but that wears the motor out more quickly and runs the battery down faster.

Main Types of Electric Bike Batteries

Sealed Lead Acid (SLA). Cheap to produce, most electric bikes in recent years have used SLAs. They are virtually maintenance-free and have a high energy density but they are very heavy (typically 30 lb.), cannot be charged quickly and will eventually die when the battery cells are old.

Nickel-Metal-Hydride (NiMH). The advantage of NiMH batteries is their ability to fast charge plus they are lighter and less toxic than SLAs whilst maintaining high energy density. Performance, however, is reduced in cold weather and they need to be fully discharged at set intervals to maximize battery life.

Lithium-Ion (Li-ion). Lightweight and maintenance free, these batteries have a longer life and can be fast charged. They are, however expensive and can be unstable so must be used with a battery management system to maintain the stability of the chemicals, charge and temperature within each Lithium cell. Latest generation Li-ion batteries using iron phosphate (LiFePO4 or LFE) are far more stable.

Lithium-Polymer (Li-Po). The lightest (typically 10-12 lb.) and newest of all e-bike batteries, these are even better than Li-ion models as they are more stable and have low levels of discharge but naturally they are the most expensive. Critically, the best LiFePO4 batteries can be recharged over 2000 times versus 600-700 timed on older Li-ion batteries.

Costs on electric bike batteries range from around $140 for an SLA to over $600 for the latest Lithium iron phosphate models.

Which Electric Bike Battery to Choose?

Price and weight are two key factors to consider but it is important to compare the performance, longevity and recharging times of each battery before purchase.

Many manufacturers reduce battery weight by compromising power output so it is important to read the small print carefully. A cyclist wanting to use an e-bike for regular commuting may well need to invest in a light Lithium battery with a fast recharge option to avoid having to carry a spare as back-up. Occasional cyclists, on the other hand, may be happy with a cheaper SLA battery.

Tips for Maximizing Battery Life on an Electric Bicycle

Electric bike batteries should be recharged after every use, not just when they have run down.
Consider buying two batteries so that there is always one available to use when there is no time for battery recharging.
If storing the battery for long periods (1 month or more), fully charge and then disconnect the battery from the charger.
Always pedal when climbing hills to help the motor and increase battery life.
Store the battery indoors overnight rather than leaving it outside on the bike – a good theft prevention option on an expensive Lithium battery!

Electric Bicycle Batteries

Whilst the technology can be confusing, compare battery weight, riding distance, recharging times and durability before making a purchase of either an e-bike or an electric bike conversion kit.Then simply follow these tips to look after the battery and ensure maximum longevity.

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