Lithium Battery Care


by Jacob Fox January 25, 2017

I thought I would write a small article on battery care and lifecycle as it is a common question that people ask when purchasing an electric bike. This will be quite basic and won’t go too much into the nitty gritty, though should be helpful to most people who are just recently introduced to the electric bike world.

An electric bike battery contains multiple battery cells combined in series (+ to - ) and in parallel (+ to + and - to -) to make up the Voltage (V) and capacity (Ah) respectively. To get the power capacity (Wh) of a battery you just multiply the Voltage (V) and the capacity (Ah). A common battery configuration is 10S 4P, which means 10 sets of 4 cells in parallel wired in series, which makes a 36V, 10.4Ah (374.4Wh) battery. That’s 40 battery cells in total! As you might imagine maintaining the health of each of these individual cells can be a difficult proposition. Though fortunately there are built in electronic systems to make this an automatic and simple process.

Over time each cell bank can get out of balance, which means the voltage of each bank is different. This causes the other cell banks to do more work to compensate for the loss in balance. The Battery Management System’s (BMS) job is to ensure that each of those cells are balanced and healthy. BMS’s are built into most quality lithium ion batteries and are highly recommended safety and management device. Each cell is balance regularly automatically by the BMS when the cells become out of balance.

A smart lithium ion battery charger (which are generally provided with the battery) will ensure that the cells are charged to maximum capacity, without overcharging the battery, which could cause damage to the cells and possibly even fire. Most quality chargers are designed to stop charging when the battery is fully charged, though I still would recommend observation and charging in a fire-retardant area to ensure reduction in damage in the unlikely event of a fire.

Each battery cell is rated for several cycles. A cycle is a discharge and full charge. 500 cycles is a common amount of cycles for a good quality cell. This means that if you use the battery each day it should last 1.37 years before replacement is necessary. Some batteries have a higher lifecycle than others.

There are some things that you can do or avoid to increase the lifetime of your battery:

Try not to discharge your battery down to 0%.

The amount that you discharge your battery is correlated to the life cycle of the battery. Reducing the total amount that you discharge your battery will in turn increase the longevity of the batteries life cycle.

Reduce strain in cold conditions.

Just like a human, getting started in the cold morning can be difficult. Go easy on the bike on cold morning/days to prevent unwanted strain on the system. Avoid going straight into full throttle or highest pedal assistance mode. Start out low and increase over time to allow the battery to gradually warm up as opposed to sharp increase in temperature.

Avoid operating in very high temperatures for long periods.

Lithium Ion batteries can suffer stress when exposed to high temperatures avoid leaving your battery in sun for long periods of time, especially when fully charged.

Maintain good charging habits.

Ensure that you charge your battery after each use or when the battery is low. The smart battery systems that are built into each component will manage individual cells.

How do I store my battery?

It is recommended that you discharge the battery down until approximately 50%, remove the battery from the frame and store in a dry, cool area. This will ensure that the battery is in its natural state and is less likely to reduce the health/lifetime of the battery. Do not leave your battery at a low charge for a long period.

 What about reducing the voltage that you charge the batteries?

There are lots of studies and evidence about increasing the cycle life of the battery cells by reducing the maximum voltage that you charge the battery to. It is said that you can double the amount of cycle life by decreasing the charge voltage of each cell by 0.1V. For a normal 36V battery that means the charge voltage would reduce from 42V to 41V. This will decrease your maximum capacity by approximately 14%, which in turn will decrease range. This can be difficult to achieve with the current battery charger as you have to monitor the voltage of the battery periodically during the charge and take it off charge once it reaches that voltage. If you wish to undertake this style of charging we recommend that you still charge the battery to 100% every week to ensure that the BMS can efficiently balance the cells.

There are many online resources and white papers explaining this information and good tips for caring for your lithium ion battery. Battery university has lot of information on all types of batteries and is a good place to start, just google ‘battery university lithium ion care’. 

I hope this helps people understand a little bit more about an electric bike battery and how to care for it. As always, I encourage you to investigate this information yourselves. If you have any further information you would like to share or you would discussed let us know.

 

 




Jacob Fox
Jacob Fox

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