The Cycle 9 e-bike LiFePO4 battery: Long life, light weight, lithium iron phosphate polymer battery pack with automatic charger.

It weighs only 8 lbs, and is compact and will easily fit in a trunk bag on your bike. It will power your ride reliably for years.

A long lasting battery that will take you over hill and dale to where you need to go. Lithium-Iron-Phosphate is the most stable and lightweight lithium chemistry used in ebikes today. Combined with extra long life, this battery is the best value your money can buy. This LifePO4 battery give you many solid years of transportation service.

Not all LifePO4 is created equal. We've searched high and low for a pack with high quality cells and circuitry that won't break down in the first year of use. You will be able to find cheaper LifePO4 batteries, but with this battery, you'll have the peace of mind of quality, backed up by a company that can help you with anything that might come up.

Available in 10, 15, or 20 amp hour capacity, so you can find the right size for your needs.

We use these every day, and haven't found another battery we'd rather put on our own bikes. We think you'll feel the same way after trying one out.

Note - At the present time, shipping regulations only allow us to ship these by ground in the continental US and Canada.

• 36 volt battery pack (42V when fully charged), compatible with most electric bikes and kits on the market
• The 10 Ah battery holds 10 amp hours of charge. That means it can supply 10 amps for one hour
• This is about 360 watt hours. It could run a 100 watt light bulb for 3.6 hours.
• It can run a typical electric bike from 15-30 miles. It all depends on how much you pedal, and how big your hills are. If you use it only on hills, you're likely to get even more mileage out of it.
• This pack weighs only 8 pounds, and is 26.5 x 9.5 x 8.6 cm (10.4 x 3.7 x 3.4 in). That's all.
• It uses the very long-lasting polymer LiFePO4 cells. These are not the less expensive and heavier cylindrical or prismatic cells.
• It comes with an automatic charger, and Anderson Powerpole 30 amp discharge terminals
• It is designated for maximum discharge rate of 3C, which means 30A for a 10 amp hour battery like this. We've found that it can output more current than that, but we don't recommend it for long life. If you have a 35 amp controller, we recommend using a 15Ah battery pack or larger.

Cycle 9 has searched high and low for the best LiFePO4 batteries, to bring them to you. We finally found LiFePO4 batteries that are light weight, reliable, and meet or exceed their rated specifications. Ever since we found these, we stopped using our other batteries, and now use these on our own bikes, every day.

We've messed around with a lot of different LiFePO4 batteries. Some of the other products we've had to deal with have given us nightmares. LiFePo4 is a great battery technology, but there is a lot more to a battery than just the chemistry.

See, all LiFePO4 battery packs are made up of a series of individual LiFePO4 cells, strung together. It is kind of like lights on a Christmas (or Holiday, if you prefer) tree. You know what happens to that string of lights when one bulb goes out? At least in the old days, it was a frustrating experience, because the whole string would stop working, and you'd have to find the bad bulb to get the string working again.

Then, some genius came up with "smarter" light strings, where the whole thing would keep operating even with one bad bulb.

Well, lithium batteries are a bit like that. Each cell strung together in a row has to do its part, or your battery "goes dark". So, even though there are claims of LiFePO4 batteries lasting 1,500 or more charge and discharge cycles, it is a lot more than just stringing the cells together (12 of them, in this pack). Unfortunately, we've seen a lot of poorly strung together LiFePO4 packs, that fail early and require time/money to get working again.

The only way to keep the cells each happy and doing their jobs, is a sophisticated piece of technology called a "Battery Management System" (BMS board for short). This battery board constantly monitors each and every cell during charge and discharge. It keeps each cell within a specified voltage range (2.2V to 3.7V), and it turns off charging or discharging if any cell is outside of that range. This is critical for long life.

Cycle 9 LifePO4 comes with an optimized charger

Now, it is not just the BMS board that is important, it is also the charger. They work as a team to make sure that each and every cell in the string is fully charged (balanced) and ready to roll. Here's another thing we discovered: most charger manufacturers and battery manufacturers don't talk to each other.

When these batteries first arrived at Cycle 9, our excitement over their light weight and small form factor quickly turned to disappointment. Batteries rated 10Ah were only giving 8-9Ah of power. We couldn't sell a "10 Ah" rated battery that really only gave 8 (though, unfortunately, we've seen a few people doing just that with their own LiFePO4 packs, because they don't test them like we do).

We put our resident expert to work on figuring out why (she has degrees in physics, computer science, and bioinformatics, so figuring out a battery shouldn't be too hard, right?). After troubleshooting, the bottom line is that the chargers were not correctly interfacing with the BMS board. Cycle 9 worked with both the battery manufacturer and charger manufacturer to get it right (before we sold any of these). And this transformed these batteries from underperforming to overperforming - typically, we are getting 11 amp hours out of one of these now.

The result is the first battery that we proudly put the Cycle 9 name on, and back it up with our Satisfaction Guarantee.

The battery comes with a 6 month manufacturer's warranty. However, we want to make sure you are happy with it, and so we extend the warranty to 1 year for any manufacturer's defects. Even after that period, if you have any problem at all, we will happily diagnose the battery, and will generally repair it for a minimal charge (sometimes for free, if we don't think it should have failed).

Or if you want the utmost confidence in it long life and trouble free operation, you can purchase our extended service plan in the options menu above, and we'll either repair or replace your battery for free if there's any problem during the service plan period (excluding misuse or neglect, only because we don't want to be replacing batteries that people did science experiments with).

How big a battery do I need?

This is probably one of the most common questions we get. There are 2 main considerations for the capacity of a battery. One is the range you want to travel. A battery with a higher capacity will take you further than one with lower capacity, but it will also cost more, be heavier and bulkier. So ideally you want to match the battery to your needs without going overkill.

Here is a rule of thumb for calculating your range. First calculate the total available watts for the battery by multiplying the voltage times the amp hours. So 36V 10Ah = 360 watts. Then divide the total watts by your motor's consumption. Now this efficiency rating is sometimes hard to come by, but for a typical 36V geared motor, we have found useage to range from 10-20 watt hours per mile, depending on how much you pedal, how many hills you have, how windy it is that day, how much weight you are hauling, etc. So 360 watts divided by 10 watt hours per mile (a conservative usage of the electric) will give you 36 miles of range. If you use the electric more and pedal less, then 360 / 20 = 18 miles of range. So this battery would provide about 18-36 miles of range. If you have a direct drive motor (such as Bionx, Nine Continent, or Crystalyte) your efficiency, and thus your range, will be higher.

Now, a 48V battery will have a higher capacity than a 36V battery, however, it also has more power and speed available, so typically the amount of watts used per mile is higher with a 48V battery unless the power is limited. When we have all that power at our fingertips, it is just human nature not to use it a little more!

The second consideration when choosing a battery capacity is what type of amperage your controller is using and what rating your battery has to supply this amperage. In addition to voltage and amp hours, batteries have a 3rd rating, called the C rating, which is an indication of the amperage your battery can provide. Multiply the C rating times the Amp Hour rating to get the MAX amperage the battery can provide (e.g. for 36V 10Ah battery with a 3C rating, the max amperage is 3 * 10 = 30 amps). This is the maximum the battery can provide. Batteries will be much happier and longer lasting if you keep them below their max most of the time. Now compare this number with the amperage rating on your controller (eg. 20amp, 30amp, 35amp, etc). This rating is how much amperage your controller is capable of drawing. If the controller is drawing more than the battery can supply, you could do damage to the battery. To get around this you can 1. get a larger capacity (amp hour) battery, 2. get a battery with a higher C rating, or 3. limit the amps your controller draws using a cycle analyst. Note that this calculation is independent of the voltage rating.

36 or 48volts?

The voltage of the system determines the overall amount of power, acceleration, hill climbing, and top speed you'll get from a given electric bike system. A higher voltage pack allows the bike to have a higher top speed, and generally more climbing power. The first thing to consider when choosing your battery voltage is your e-bike controller. The e-bike controller (the brains of the system, which converts the direct current from the battery into pulses that operate the motor), must be the right voltage for your battery. You can't hook a 72V battery up to a 36V controller, unless you like the smell of burnt electrical parts. Some controllers can handle a range of voltages, allowing versatility.

Without a chance to try out an e-bike it is sometimes hard to determine just how much power is needed for your particular hill. So here are some stories about our experience with different ebikes which might help. Cycle 9 co-founder, Dr. Morgan says about her eZee electric kit with 36V:

 I use an eZee at 36V on my daily commuter, which is a "Surly Big Dummy" on which I carry my daughter, computer, groceries, etc.  Our typical load on that bike is about 280-320 pounds (total), and I have several steep (but short) hills.  At 36V, the eZee does a great job of taking the grunt out of those hills, and at 48V it is downright zippy.  The other day I tried the ride without motor assist, and with that kind of load on the bike, it was a real grunt - I am in pretty good shape, but was going up the hills at 4 miles per hour standing on the pedals.  My electric assisted speed on the same hills is 8-12 mph, with a lot less pedaling effort.

When she wants higher speed, she goes with a 48V battery, but the 36V does a great job of climbing the hills as long as pedaling is acceptable. Here is what Cycle 9 co-founder Elise has to say about her bike with BMC V2 motor and 48V battery:

I usually use a BMC V2 motor with 48 V battery on my daily commute, which is about 7 miles over hilly terrain. Often, I am in a hurry and running late, so I tend to run full tilt a good portion of the way. With the 48V battery I barely even have to shift down out of top gear when going up and down hills on the highway and in-town on major roads. Usually I can blast up at 18mph+ and I typically keep my speed between 18-22mph for the full commute with only moderate pedaling effort. When I am not in a hurry, I use the bike at only half throttle or less for most of the ride.

If you are looking for higher capacity or different voltages, we have the same great battery in different configurations on our batteries page.