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Batteries and battery packs, the lifeblood of your electric bicycle
Plug and play?... Not always that easy and certainly not very simple for most of us.. Or is it?
A good lithium battery pack can cost as much, and often even more than the rest of your electric bike kit. Picking the right pack for the job is very important. Below, you will find information to get you on the right path to ebike happiness!.. Read-on!
Back in the late 90's when I first started learning about ebikes and related electric bicycle conversion kits, I found myself looking at a website offering a lead acid 150$ battery pack and then scrolling downwards, a nimh pack, the holy grail option at 1200$ ! .. Say what ? … nearly 10x the price for only double the range? That can't be right ?. Can it ?
The big question: how do you get the most battery for your hard earned money?
Well, the first step is to learn about and get an understanding of the basics regarding battery packs, then determine what you need and what you can afford. The last thing you ever want to deal with, is being far from home and suddenly losing power! Going out for a ride with confidence, knowing that you will have a great time, enjoying the ride, the sights and sounds and then getting home without any stress is the ultimate goal and will result in you wanting to do it over and over again.. Every day.. "Ebiking" is a way of life for some of us, equipment failures and getting stranded far from home, not on my list, at any price!
Range, how far can you go on a full charge? Well, ladies and gentlemen, my personal number one pet peeve, range estimates! Every company, website and sales person struggles with this, on one side you have the desire to claim the best case scenario as it makes the best sales pitch, but on the flip side, if it looks too good to be true, it usually is. Fact is this, expect typically 20 miles / 32 km from an average 6 to 8 lb lithium battery, that is the universal truth and pretty much the most honest statement a company can make.
Li-ion battery weight range (mi)
6-8lbs 20mi (32km)
More range and less weight are not possible in real life, until battery tech improves significantly, those are the realities, for everyone. 6 to 8 lbs for 20 miles of no-pedal range at 20 mph. No matter what battery pack and who sells it, get the real weight and base your range on that information.
Those who claim " 100 miles on a single charge " either have a 40 lb ($$$$$) battery, or they intend you to pedal for 80 miles, then turn on the power for another 20... If any battery pack could deliver 100 miles of no-pedal range on a single charge and weigh less than 10 lbs, gasoline would cost much less. On some ebikes equipped with pedal sensors and no throttle at the handlebars, that require you to pedal for power to flow, range estimates can be true at very low power settings. However, given the rider is pedaling and providing human power, this is not no-pedal range and makes a significant difference.
If your ebike has a handlebar throttle, that allows the motor to run without pedaling, power consumption is much greater. It's important to understand how your ebike works, a 500w kit does not use exactly 500w, all of the time. If you pedal without using power, your battery remains fully charged until you use it, it is entirely possible to ride a whole day on a charge by using it sparingly. That being said, most people ride with the throttle firmly pinned to " max " and in this fashion, expect 20 miles from a 6 to 8 lb battery in one hour before you run out of power on most bikes. (*insert fine print here)
What is a battery pack? .. Well.. It's a pack of batteries! A pack is made of a number of smaller battery cells all stacked in a specific way to deliver the required power that your ebike system needs to function. You must pick the right pack, for your application!
Volts and amps: without going into too much confusing detail, voltage is what pushes ( speed ) the flow of electric energy, while amps is a measure of force. Typically, higher voltage electric bikes go faster, while higher amps require thicker gauge wires and/or more powerful and larger battery packs. Combination of volts and amps equal watts.
Ok, time to crunch some numbers and get down to the nitty gritty of it. All batteries and battery packs will have fine print, listing various things of high importance, put on the bifocals and squint, expect to find things like :
Volts: used to describe how fast electrons move, more voltage = more speed !
Amps: how wide the road is, more lanes, more cars can pass at the same time side by side...
Watts: the combination of volts and amps ( volts x amps = watts )
Amp hours: should always be listed, typically 10 to 20 amp hours ( abbreviated " ah " ) a measure of how many fixed number of amps a battery can sustain for 1 hour.. ( c rate ). Or, double the amps for half the time.. Or half the amps for two hours.. Etc.
Watt hours: this is a far more accurate way to know how much usable energy is in a given battery pack ( abbreviated wh ) when available, this is the number to look for! Also, you can translate it into how many watts, continuous, for 1 hour! A 500wh battery can deliver 500 watts for 1 hour or 1000w for 30 minutes.... Or 250w for 2 hours .. Etc.. Most ebikes do not use power at an exact level, continuously, so this does not directly translate into ride time, but you can quickly see how a larger battery with more energy (capacity) can deliver lower power levels for longer periods of time, and go further on a charge.
Load run time (hours)
500 wh 250w 2 hours
500 wh 500w 1 hour
500 wh 1000w 30 minutes
A word of caution, some vendors are prone to bending the truth and "Over-promise" when it comes to range expectations. Be sure to do some research before you buy, ask the right questions and by from a vendor that provides range estimates in relation to your weight, bike, intended use and intended input.
Ah vs wh: this can get confusing, but it is very important to understand the difference. Amp hours (ah) means nothing unless you factor in the voltage. Watt hours (wh) is far more important because it factors in the voltage and the amp hours together and determines how far you might go on a full charge. Not all packs are labeled and/or constructed the same, so be careful and pay close attention.
Wh example: 36v 10ah = 360wh and 48v 10ah = 480wh
A word of confusing wisdom, if you consider a bike that can run on both 36v and 48v, that goes faster on 48v when run at full throttle. The faster you go, the more energy you need!
So a 48v battery with an extra 120wh, compared to the 36v pack will not always give you more range, if you go faster than the 36v bike would be going at full throttle.... But who can resist going faster? .. But otherwise, the more wh you have on the bike, the more range you can expect from it.
What does all this mean to you? With just a bit of knowledge, you can make better informed buying decisions, put together the proper kit pieces and ride happily ever after without running out of power and not buying a lot more than you need!
Size, weight and shape, three things to consider when making a decision on what pack to buy. It has to fit and not be too heavy, and should look good once installed on your bike. You will likely not find all the ideal factors in a pack but some are vital, while others are not as much.
The most common mistake that many ebikers make is to want a huge battery, this is all fine and great until you have to figure out how to mount it on your ebike, and then it gets worse when you need to carry it up a flight of stairs or put it on a bike rack!
Be realistic and you can save yourself a lot of headaches and money, also end up with the best ride possible for your needs!
After building 100's of bikes for people short and tall, big and small.. I have found that the key to an ideal setup is to have the lightest and smallest possible battery pack that will get the job done. It might seem like a good idea to have a pack with twice the energy you need so that you never run out on even your longest trip, but this can be a mistake, too often repeated!
First step, determine your needs. Most people, myself included, rarely go more than 20 miles at a time without stopping ( 32 km ), usually much less. I do, however, go out for multiple rides in a day, very often! Going out for a short errand and then plugging in the charger can be quick and convenient, and 30 minutes later I can go out again with a full charge if needed. The point I'm making here is that an ebike with a small battery pack is lighter, costs less, is far more enjoyable to ride and can be charged quickly while providing all the range you need even if it's not all on a single charge.
That being said, if your needs are more utilitarian in nature, like an electric trike hauling a trailer of groceries or children , or in my case a 70 lb dog, up some major hills against strong wind. Well, in that case, you not only need a bigger battery, you need a bigger motor, stronger bike, heavier, more expensive, you get the picture? But, if that's what you need, larger capacity packs are available and will get the bigger jobs done!
A vast majority of the time, a lightweight ebike is what most of us need. On this type of electric bike, on typical fairly flat roads, not much wind or none at all (because a bit of wind, can make a big difference in energy consumption!), while barely pedaling, like very leisurely but not working up a sweat, on good and pumped tires, typical 200 lb or less rider, expect burn rates of 10 wh/km .. Or 17 wh/mile on average. It can be much more or much less depending on countless factors but this is a realistic number to start with.
For example, a 36v 10ah battery pack with 360 wh of capacity. (36 volts times 10 amp hours equals 360 watt hours). This pack would in theory provide 36 km of range, or 22 miles, from a full 100% charge.
Now, before all you engineers light me on fire for averaging numbers and being loose with specifics, I am doing this for simplicity reasons, your actual mileage will vary. Very few people have the tools to measure a battery pack's capacity and some vendors may take advantage of this.
Voltage (v) capacity (ah) energy (watt hours) range (mi)
36v 10ah 360 watt hours 22mi (36km)
Voltage: most ebike kits are rated for a specific voltage range. A typical 36v ebike needs a battery that delivers power between 42v to 30v. A 36v pack, at 42v is fully 100% charged and holding as much energy as it can and at 30v it should shut down and stop giving power before causing permanent damage.. More on bms (battery monitoring system) in a bit. The common " 36v" number is an average operating voltage or sometimes called nominal voltage.
Electric-find.Com says: "Voltage, nominal. A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.G., 120/240 volts, 480y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.May 28, 2009"
Some ebike kits have a wide operating range like 36v or 48v, so be aware and pick accordingly. Most ebike kits with displays that show battery charge levels with a series of led lights can only work at that voltage, if in doubt, ask the vendor!
E-trikekit led display 2012
Voltage is what drives the motor's peak rpm, if the same motor is given a certain voltage, it will turn at a given speed, increase the voltage and it will spin faster!. That being said, electric motors are made to turn at a certain rpm for a given application, determined by its construction.. The bottom line here, a 36v bike will go faster with a 48v battery pack (if the electronics between the motor and battery are compatible). The motor itself does not care, but the rest of the components do; controller, throttle, display, etc.
Amps: in order to pick a proper battery, you need to know about your ebike " controller ", this is something found on every single ebike, it does exactly as it's called, it controls the power between the battery and the motor by pulsing on/off very quickly ( aka : pwm, pulse width modulation ). If you are at a complete stop, and just jam the throttle on full, the controller will step in and way " woooah.. There buddy... Hold on.. Not so fast... And will set a limit of how many amps are allowed to flow to the motor, it's maximum amp rating. Why does this matter in terms of picking the proper battery pack? Because you must have a battery that is powerful enough to deliver those amps without overheating, shutting down, blowing a fuse, etc.
Generally, a 10ah battery will work well with a 20 amp controller or less. If you know some of the specs but not all of them, you can do the math but once again be sure you have the correct and honest data to begin with. Sometimes some controllers have " watt ratings" while others will show "Max amps" and this can lead to confusion.. When a controller is rated for watts, you need to know if this is "Maximum watts" or "Continuous watts" with a higher peak. Your battery needs to safely handle the "Peak" or "Max" when needed.
Quality: a battery pack is only as good as it's weakest cell, and as durable as the thing you put it in! Back in the old days (oh god.. Did I just write that ?.. Urgh) getting a lasting pack was pure random luck and a rare thing at that. A pack that lasted a few seasons or survived a 6 month vacation on a bench without self-discharging to death was a rare thing. Battery packs and cells have improved greatly and today in 2017 we finally have reached a point in evolution that reliability and quality packs are readily available, it's the finer details that matter most, like getting one from a reputable vendor who will back a warranty and who sells enough of them quickly to keep recently built packs in stock.
Bms and chargers, to protect and charge your pack. Lithium batteries are light and durable but they must be used within their specified limits. In order to insure a long life, battery packs should contain a bms, aka: battery monitoring system. It stands between the actual battery and the power wires, monitors all the voltages of cells within and also typically watches how many amps are flowing. If any limits are reached the bms should intervene by cutting off the power safely. In a perfect world, the bms will sit there and do nothing but if you do ride until you use up all the energy available, it will shut you down and prevent any damage to the battery cells. Similar situation with the charger, the bms will allow the charger to do it's thing as long as all the cells are in harmony and within their limits, a quality charger is very important and often completely overlooked, I have witnessed great battery packs destroyed by horrible chargers.
Mounting your battery pack to your ebike can be a challenge, there are ideal locations and there are convenient one's, rarely do they come together as one. Depending on your bike of choice and riding style, inside the frame and between the wheels is ideal for the best possible weight distribution and ride comfort... While on a rear rack or saddle bags is easy and convenient but can have an adverse effect on handling ( and looks .. Personal opinion I suppose ). This is where shape and weight come into play!
Battery packs in aluminum cases and mounting brackets make the task of mounting to your ebike much easier while also protecting the pack from impacts, but it adds cost, weight, and bulk. A pack with simple shrink wrap is less expensive but care must be taken to mount it safely in order to prevent crushing of the rather fragile cells or damage due to vibration while riding, or when the bike tips over and hits the ground (not if.. But when!)
Too small? Yes, this is a possible problem to consider. A battery that can run for an hour of riding under worst case situations is usually sized properly. A larger capacity battery will not have to work as hard as a smaller battery when used on a given bike. A 10ah battery delivering 500w continuous will run for half the time of a 20ah battery pack. There are many other factors to consider (c rate and internal resistance of cells used in a pack) .. But this is beyond the scope of this text... Google "C rate lithium battery"
Battery care: make it last, learn about proper use and care, even with a bms that will shut down the power safely, it's always best to keep charging and try to never run the pack down all the way, this applies to all battery types. I personally like to always leave for a trip on a full charge whenever possible, and if I know I am stretching the limits of my range, I make more effort to pedal a bit harder and conserve energy. Do not charge a frozen battery pack, bring it to a warm location and give it time to warm up, if you are comfortable in a tshirt, so is your battery. Using your battery pack in cold weather is ok, expect a drop in range and performance during winter months but no harm done. Let it warm up before you charge if it was stored in the cold prior.
Opportunity charging is also perfectly ok, if your trip is a long one and you stop for a coffee or a short break, plug in the charger and grab some power, it may not fully charge but will extend your range if needed! And in case anyone asks, electricity from the wall costs about 10 cents per kilowatt hour (1000wh = 1 kwh) so your 360wh battery pack only holds less than 4 cents of power on a full charge!
Legal shipping of your pack, this is a highly controversial topic, given the significant amount of energy these battery packs can contain, there are regulations and proper ways to package, ship and handle them. Reputable vendors will proudly advertise about shipping legally aka: "Un certified", a very expensive process to insure safest possible shipping. Many smaller vendors do not ship un certified and do so illegally. In the event you need to return a pack for warranty, you would be doing so as well.
Energy density is how much energy a battery can hold for a specified volume (wh / liter), unlike typical liquids where 1 gallon occupies a given space. Two battery packs of identical size can contain different amount of usable energy. For example, in earlier days of lithium a typical 18650 cell would hold about 1000mah (one thousand milliamp hour "Mah" = 1 amp hour "Ah"), fast forward to today as of this writing in 2017, there are cells available that are the same size (18650 cells are 18mm wide and 65mm long) and can hold upwards of 3500mah! So for the same size box, a modern battery pack can deliver 3x the range vs what was possible 10 years ago.
Lead acid vs lithium, lead is less expensive at first. If you just cannot afford a proper lithium battery pack, lead is the least possible option available to get you on the road. Consider a 6 lb lithium battery pack can go as far as a 30 lb lead acid battery of equal voltage.
Battery chemistry capacity weight range (mi)
Lead-acid 15ah* 30lbs 20mi (32km)
Lithium ion 9ah 6lbs 20mi (32km)
*we are considering a 15ah lead-acid battery against a 9ah li-ion battery here because the usable capacity (in typical high-amperage use on an e-bike - see peukert's law) of the 15ah lead is only about 9ah (66%) - note that they have the same range*
As you can see there is a lot to consider if you really want to delve deep into lithium battery packs that are made to power electric bikes. Overall your biggest consideration as a buyer should be to know how to care for your battery pack, do your research and buy from a reputable vendor that is shipping a un certified pack legally and most of all... To buy the pack that best suits your e-bike riding needs!