Electric Bike Battery Basics: What are these Volts & Amp Hours?

Electric Bike Batteries: They aren’t that complex.

Alright!  You are getting excited about the electric bike scene and you start looking around at some e-bikes, but what do volts, amp hours, watt hours mean?  Well I aim to answer some of these questions for you here!

The terminology for electric bike batteries can seem a little foreign at first but I think the following will relate it to some typical car terms that may make more sense.

Volts (V) = HorsePower!

Volts = Horsepower!

That is a pretty simplistic way of putting it but it is the closest analogy to a car.  Electric bike batteries typically come in 24V, 36V, 48V, and 72V batteries.  More volts = more POWER :)

Here is another analogy: electricity is water.   If it is water flowing through the wires (tubes), then higher voltage means that the water (energy) moves faster, and through a smaller tube.

The typical battery is 36V on most e-bikes with some at 24V and some at 48V.  The electric bike manufacturers spec these because they provide a good power to cost ratio.

When you get up into the 72V range you are looking at a custom built electric bike because a 72V battery will generally make a bike that is powerful and may not be classified as a traditional bicycle.  72V batteries are significantly more expensive too.

Here is another thing to consider when building or using a high power electric bike; being SHOCKED!  Human skin can insulate you from shock up to something in the area of 40 – 45 volts. 72 volts is a shock hazard, and in some places that is a regulatory issue.  It is always a safety concern.

If the power output (watts) or the max speed of an electric bike goes above the allowable (250 Watts, 25 km/h in Europe / 750 Watts, 20 mph in US) then the e-bike will be classified as a moped which generally requires registration, insurance, license plate, etc.

A little background on controllers…..

Ultimately the electronic controller of an e-bike limits the maximum power output and the maximum speed of the bike.  If you buy a stock electric bike in your country, you will most likely be buying an electric bike that complies to the max power and speed limits to be classified as a bicycle (this is not always true though!).

If you are building your own custom electric bike you will want to be aware of what controller you are buying if you want it to still be classified as a bicycle.  It is possible to create an electric bike that is too powerful or too fast with a lower voltage battery if you have a controller that allows it.  Just something to be aware of if you are building your own electric bike.

Amp Hours (ah) = The Gas Tank!

Yup, it’s generally that simple.  The more amp hours you have, the more range you will get with your electric bike.

Now one thing to be aware of is that every manufacturer will claim that their bike has incredible range :)  You may see an e-bike with 36V 10ah battery that gets 25 miles and then another with the exact same battery that gets 50 miles of range.  “Your mileage may vary” is the car terminology for average miles per gallon, but I think that crosses over to e-bikes range claims!

There are a lot of factors that affect the range of the electric bike, such as:

What power assist setting you are using?  Most power assist bikes have 4 assist levels.  Some e-bikes just have a throttle that you can vary the assist with.  This is pretty common sense, but the more assist you use the less range you will have.

Are you climbing a lot of hills?  Range goes down.

Are you riding into a lot of headwinds? Range goes down.

Are you carrying heavy cargo on your bike? Range does down.

Some bikes may have a very inefficient motor (lost energy in the motor due to friction, etc.) that causes decreased range, but these days most electric bike motors are fairly efficient (there is room for improvement!)

What is the condition of your bike?  A well adjusted bike goes farther i.e. well lubricated chain, proper tire pressure, etc.

What is your tire pressure?  Lower pressures = less range.   There is a nice balance between too high a pressure (not comfortable) and too low a pressure (not efficient).  50-60 psi is a good pressure range for street riding.

Are you pedaling at the right times?  Pedaling at critical moments (when accelerating or climbing), you will go farther.

Pedal more => More range and better health :)

If you are concerned with range I recommend going with a large capacity battery pack.  Some electric bike manufacturers have use a standard 10 ah pack with an option to upgrade to say a 15 ah pack.

Watt Hours?

I am afraid I don’t have an car terminology equivalent for this one.

Basically it is the the combination of the volts and amp hours to give you the total energy in the battery pack.  You may see this in the specifications for an electric bicycle but it is not as common as the volts and amp hours specs.

Volts x Amp-hours = the amount of energy in the battery, or watt hours (WH).  It is a way to compare batteries of diffeerent voltages or AH ratings.

For example:

Bike #1 has a 24 Volts and a 20 AH battery = 480 watt hours.

Bike #2 has  48 Volts and a 10 AH battery = 480 watt hours.

Both bikes have similar energy on board. And if they have roughly equal motors and riders, they will probably perform in a very similar fashion. The higher voltage bike may accelerate faster and climb better – at the expense of some of that energy.

Another bike has 24 Volts and a 6 AH battery = 144 watt hours. That bike is not going to go nearly as far as the other two.

That’s it for now.  Stay tuned for more e-bike basics.

-Pete

P.S. Don’t forget to join the Electric Bike Report community for updates from the electric bike world, plus ebike riding and maintenance tips!

Comments

  1. Trukerdutch says

    Your explanation on electrical terminology is very good, & appreciated. My wife & of 43 yrs are retired recently, & if we can afford it we would like to get one of the ‘Pegego’ Electric Tandem bikes this summer. Have been catching bits of news here & there on types of batteries that may be available. The voltage would be in the 48-volt arena, and will need one that will take us as far & long as possible. We live in an area that has mostly flat roads & small knolls and rises. No big hills. Lithium-ion/phosphate. Lithium-manganese. And latest one is Hyrogen/extended range battery. Would the latter one be the best for us? It seems to be the latest hi-tech option & we need to know how expensive & dependable as well as safe it would be for us. The Dutchman and the Mrs.

      • says

        The Pedego Tandem is in stock and selling out fast. It has the same proplusion system as the Pedego Interceptor – 48 Volt Motor, Battery, Controller and Throttle. For extended range, the best solutions are 1. Carry and extra battery and/or 2. Carry a charger with you. The 48 volt LifePo4 battery is 10 Ah and should take you 20-30 miles per charge with minimal pedaling. With 2 batteries, you can go twice as far. Call us anytime at (800) 646-8604.

  2. Zazzzzisme says

    thank you.. nice explaination… now another question. i have an e bike and love it… i also have a scooter/bike and i need new batteries. 4 12v 12amp. and i am having a hard time finding them here in san diego. everyone wants me to bring in the batteries i have. why cant they just tell me if they have 12v 12a batteries. then i have to connect them. is there one battery that will take the place of 4????

  3. Garen Elston says

    I just bought a new 48 volt, 20 amp hour LiPo4 battery from China for my bike. I charged it with the provided charger. After charging, it is up to 60 volts. Is this how much it should have?

    Thanks,

    Garen

    • Pete says

      Hi Garen, Normally a 48 volt pack would be in the 52 volt range when fully charged. That pack does seem to be a bit high. Check with the store or manufacturer who you bought it from to see if they think that is strange.

  4. says

    Thanks for spending the time to educate. I own a GT004 green power bike that I bought thru Craiggs List. The guy does not return my calls. I have been trying to find a maintenance manual to service it but have not had any luck online. The closest service area is too far for me and I call them but they also are not returning my calls. their number is 718 200-6967. Anyway I hope my info facilitates someone. I know that they are in Flushing, ny which is in the borough of Queens. I got through one time but haven’t been able to since. I need to service my brakes. If anybody has some ideas or info please share it with me/us. Thanks again for this blog. Great stuff!

  5. says

    This is really over simplistic. One thing that I think you should have talked about is that the higher the voltage is,the more cells you need and the easier it crosses your skin. The more cells you have, the more points of failure you have. Ideally, you want 4 separate cells for a 48V bike that are not packaged in a “battery” (A battery is a group of cells). What can happen in a sealed “battery” is one of the cells can become discharged and then have their polarity reversed causing that particular cell vent and to become permanently damaged it’s capacity permanently diminished, which causes the problem to happen more frequently. By have 4 separate 12v cells, they can all be charged independently and replaced on an individual basis based on the condition of the cell via the smart charger. You can also use the charger to make sure all 4 cells have the same charge (if one is diminished) which will keep that bad cell from venting again until you can get a replacement. Also, having higher torque at the low end (with higher voltage) causes much more heat in the motor at the high end. Higher voltage does reduce the thickness of the wiring needed both on the bike frame, controller and the windings in the motor, but like I said, these thinner wires will heat up faster when going very fast or climbing a hill.

    Batteries are incredibly complex and there are entire books about batteries. The same battery can go 20 miles one day, 18 the next and 22 the day after that.

    • Pete says

      Hi Chris, Thanks for the detailed info. And yes batteries are very complex. My goal with this post was to convey the basics of batteries for people who are new to e-bikes.

    • says

      No thanks, Chris. If your 4 cells give (nominal, not actual) 48V, then you’re using lead-acids and clearly off the 21st-century standards. Not even NiMHs even. Furthermore, multi-cell strings push the problem back to the BMS computer, an entirely solvable problem. Cell balancing- bottom AND top- should be standard in any BMS worth buying today.

  6. Garen Elston says

    I have a 48v 20amp hour LiPo4 on my bike that I’ve rode about 15-30 miles a day for about 45 days. The farthest I’ve ridden it on a charge was 44 miles before it cut off. I am very happy with it. It has always charged up to 60 volts and then went down a little after about one mile of riding due to surface charge. However, when I took it off the charger today so I could go for my ride, it had 67 volts. After I rode it for 15 miles, it was finally down to 53 volts which is where it is usually at after only about 5 miles. Can someone explain to me why it is now charging up to 67 volts?

  7. Dan says

    Hello all.!!!
    I am looking for a Big, Stout Electric Mountain Bike that can handle me. The one I just bought for 375$(cheap I know.lol) I BROKE!! I am 6ft 5inches and 310lbs. I need one of these as I have an injury from years ago that stops me from Hiking like I like to do. I am looking at the Busettii 60 Vortex. Can anyone out there tell me about the Vortex, the Busettii Company, if they are a Good, reputable Company and or where to look for what I need. Thanks so much!!
    dAN.

  8. says

    hi, are there any open source Battery Management Systems that are suitable for users to alter the performance etc of an e bike. that work with all providers systems?

  9. Kevin Bergin says

    I have 2 mini electric bikes one of which appears to have a battery which will not charge I have heard it may be asleep. It is 24v 6ah and I can’t seem to find a replacement. Is it ok to use a li-ion battery of different ah value. Pretty sure motor is 230W. Thanks for any help.

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