Complete E-Bike Battery Care Guide

By Ravi Kempaiah

The revolution in electric cars and consumer electronics (phones, laptops) has happened because of the developments in lithium-ion battery technology. It is the exact same technology that led to e-bikes becoming mainstream. Batteries were, and are, the bottleneck when it comes to realizing fossil fuel-free transportation and the cost of Li-ion battery is continually coming down.

One of the crucial drivers in this revolution is the improvement in energy density and cycle life of Li-ion batteries.

With companies like Uber, Ford, GM getting into the business of pedal-assist bikes, year 2018 marked a turning point in the e-bike industry. Companies like Bosch, Yamaha and Shimano are leading the way, producing very sophisticated drive systems. As more and more e-bikes get into the hands of consumers, we thought an in-depth article on the best practices of caring for your bike’s battery would be helpful. 

REMEMBER WHEN…?

Just 15 years ago most of us did not have a phone that had GPS, WiFi, 16MP camera and eight-core processor. Such power-hungry features need enormous power, and the crucial factor that enabled such electronic revolution are the Li-ion batteries. They pack a lot of energy in a small form factor, can last a couple of years with good care and deliver reliable power in a lightweight package.

“You can double the cycle life of your battery by charging it only to 80 percent.”

Given that we are all cut from the same cloth and, similarly, most e-bike batteries are made of 18650 cylindrical cells. These cells are manufactured by companies like Panasonic, Samsung, Sony, etc. Just like any other battery, they have an anode, a cathode and electrolyte. The capacity of these anodes and cathodes to host the Li-ions and the engineering design accounts for a long cycle life and high-energy density of modern-day batteries used in cars and phones.

For example, Nissan Leaf has manganese oxide-based cathode, while Apple’s iPhone has a cobalt-based cathode. The energy densities differ based on what kind of chemistry you end up using. For example, let’s say you just purchased a Trek bike with a Bosch PowerPack 500 battery. The battery consists of 10 cells in a series, and four of those modules are connected in parallel. Each cell has a jelly roll of anodes and cathodes that produce the desired voltage and current required of the cell.

Have you ever wondered why your phone or laptop battery dies after a year, while some electric cars and hybrid car batteries seem to last 8–10 years (Prius battery lasts about 250,000 miles or more, and the Tesla Model S has an eight-year, 100,000-mile battery warranty), whereas our phones and laptops need constant recharging? If you take proper care of your e-bike batteries, it will last four to five years instead of one or two.

WHAT’S REALLY GOING ON?

Fun fact: It’s the tiny Li-ions that shuttle back and forth between anode and cathode. They constitute < 2 percent of the cell weight (this ratio is comparable to the amount of salt in a salad.) This misnomer has stuck, and we continue to call them Li-ion batteries, but in reality, nickel, aluminum and other materials constitute the bulk of your battery.

HOW TO CARE FOR YOUR BRAND-NEW BATTERY

Most e-bikes run on either a 36-volt or 48-volt drive system. First, make sure you have the right charger and it works fine. If you purchased an e-bike online, then you may want to be more cautious, as batteries end up in shipping containers and in warehouses for a long time and do not receive proper care.

Plug in your battery to the charger and let it charge all the way. Once fully charged, your charger should indicate this in some way (e.g., an LED will turn from red to green). Once fully charged, you may want to test ride and make sure there is no unexpected voltage sag. 

BATTERY BEST PRACTICES

The e-bike industry is rapidly evolving and, unfortunately, most manuals are outdated except for a few leading companies like Bosch or Yamaha. On your e-bike manual, or your dealer who may not have the scientific background, may say to top it off after each ride. Well, yes and no. If you don’t care about the longevity of the battery, just charge it after each ride, the high-voltage cutoff (HVC) in the battery-management system (BMS) shuts it off after it reaches 100 percent (42 volts for a 36-volt battery system or 54.5 volts for a 48-volt battery system). 

This practice may provide roughly 400–500 cycles before there is a substantial degradation in the cell chemistry. However, if you do a few simple things, your battery may last longer than two years. This is also one of the reasons most e-bike manufacturers only provide a maximum two-year warranty instead of eight years. 

A Tesla 80-KWhr battery pack costs approximately $40,000. That’s roughly $500 for each Kwh (kilowatt-hour). Two 500-Wh (watt-hour) packs from Bosch (1 KWhr) may set you back almost $2000 (four times the cost of a similar-sized Tesla pack). One may argue that Tesla has economies of scale and better thermal design, but price per pound, e-bike batteries are a lot more expensive than car batteries. So, it may be wise to understand how things work and how to enhance the life of the battery.

TEMPERATURE TANTRUMS

Do not expose your battery to very high temperatures (above 105 degrees Fahrenheit) for prolonged periods of time. High temperatures promote parasitic reactions within the battery and cause capacity loss. Leaving the battery in the trunk of your car on a hot summer day is one such example. If you do it once in a while, it’s okay, but repeated usage can lead to premature aging of the battery.

Do not charge your battery when it’s really cold. Let’s say you left your battery in an unheated garage in the dead of winter; you may want to bring the battery inside your home and wait till the battery reaches room temperature before charging. When it is really cold, the electrolytes become very viscous, and the Li-ions have to push through a thick cloud of electrolytes. It’s like driving your car in a sea of thick honey. It slows the ions down and leads to breakdown of the electrolyte component. 

Charge your battery when it is not too cold or too hot. Let’s say you just came back from a 50-mile ride and the battery is pretty warm (you may not be able to feel it by touching the plastic case, but it does get warm). Leave it for 30 minutes so it is back to room temperature. Ideally, charge your battery so that it does not sit fully charged for hours. So, if your morning commute starts at 7:30 a.m., either charge your battery to 80 percent the night before or early that morning. Leaving the battery at 100 percent quickly degrades the chemistry.

Charge your battery as such that charging rate is less than 0.5C (always prefer slow charging versus ultra-fast charging). That means, if you have a 500-Wh battery pack, it takes two hours or more to fully charge it. Did you know that Tesla recommends not using their supercharging station very frequently? If you have an option to charge using a 4A charger and a 8A charger, use the 4A one. 

THE TIMING

“I have a [Bosch/Yamaha/Brose/Shimano] battery, and I don’t know when it reaches 80 or 90 percent while charging!” Well, that’s perfectly understandable. If you intend to use your bike soon after charging your battery, then it’s fine to charge all the way to 100 percent. If you are unable to use it right after your charge, charging to approximately 80–90 percent can be beneficial. You can do this by stopping the charging process when the battery reaches the last stage (constant voltage mode if your battery has five LED bars to indicate the charge state, then stop charging when it reaches the fifth bar; it doesn’t need to be exact, and don’t worry too much about it).

You can double the cycle life of your battery by charging it only to 80 percent. Here is a neat infographic from Grin Tech in Canada, one of the innovators in the space. They even developed a smart charger for this purpose called the Cycle Satiator (www.ebikes.ca/product-info/cycle-satiator.html).

IF YOU DON’T HAVE A SATIATOR

That’s perfectly fine. You can just use the charger that came with your bike (most generic 2A chargers are made by Modiary in Shenzhen, China). Try to keep the state of charge (SOC) between 20 to 80 percent if possible and enjoy your bike.

A simple rule of thumb is that if you can drain your battery within an hour (1C discharge), then it’s time to take a step back and rethink if you are causing aggressive battery wear and tear. If your commute or riding pattern takes two to three hours of use before you can drain the battery to 10 percent, then you’re fine. There are other cheaper options out there that do a similar job.

TWO KEY FACTORS

If you are interested in maximizing battery life, be mindful of these two parameters:

1.) High temperature = BAD for Li-ion cells. So what is high temperature? Anything above 40 degrees Celsius or 105 degrees Farenheit (trunk of a car on a hot summer day or exposing the battery to direct sunlight in a place like Arizona).

2.) Time (days or weeks) spent at high voltage = BAD for Li-ion cells. You charged it 100 percent and you’re going away for a long weekend. This may not be a good idea. If you do this once in a while, it’s all right, but repeated usage (charging to 100 percent and leaving it in that state for long periods of time) can accelerate battery wear.

STORING YOUR BATTERY

It is best to store your battery at room temperature (cool, less humid conditions) and at 50-percent charge. If that’s not possible, just avoid storing at 100 percent. Every battery degrades over time. There is something called “calendar aging,” which is the natural process of electrochemical degradation, and there is “capacity fade,” which occurs because of repeated charge/discharge cycles. A scientific article on how calendar life aging and conditions affect the degradation have been linked. Basically, what they are saying is degradation is minimal in the 30–70-percent zone (www.sciencedirect.com/science/article/abs/pii/S037877531301241x).

Store your battery away from hazardous materials like acids, corrosive industrial solvents and any oxidizing agents.

WINTER BATTERY CARE

Did you know that electric cars can lose up to 30-percent range in cold climates? This is because of the increased resistance in the cell electrolytes, but come spring, the range is regained. For this exact reason, cars like Tesla have an advanced battery cooling/heating system that always keeps their pack in approximately 70-degree temperature.

To keep the warmth in very cold conditions, it is advised to use neoprene sleeves for your battery. This not only keeps the battery from dirt, mud, water, salt, etc., but also provides a temperature cocoon.

It can be purchased from the Fahrer store (www.fahrer-berlin.de/en/e-bike/), or your dealer should be able to get you these.

SUMMARY

• Charge your battery to 80–90 percent to get maximum cycle life. 

• Get the largest battery possible for your e-bike, so you can still get decent range and a very high cycle life by   limiting the charge voltage.

• Avoid exposing your batteries to high temperatures. Store your batteries in a cool, dry place at 50–60-percent charge

• Do not charge in very cold or very hot temperatures. 

• Time spent at high temperature and high voltage = BAD for the cells.

• Batteries degrade either way, and we all come with an expiration date, so make sure to ride your e-bike as much as possible.

ABOUT THE AUTHOR

Ravi Kempaiah knows a thing or two about batteries. He is pursuing his PhD in mechanical engineering at the University of Illinois and focusing on developing advanced battery materials for his thesis. He is also an e-bike enthusiast and the current Guinness World Record holder for the longest journey on an e-bike, which we featured in the April 2018 issue.

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