Step 6: Batteries

Picture of Batteries
This motorcycle is powered by four off-the-shelf batteries. They are Optima Yellow-Tops, rated at 55 amp-hour capacity, and cranking current of nearly 900 amps. They are AGM - absorbed glass matt. That's a style of lead-acid battery that is sealed up and the electrolyte is soaked into coils of fiberglass matting. They cannot leak, spill, or slosh around.

While there are other types of batteries available, this seemed to be the best combination of price and performance for my project. "Flooded" lead-acid batteries are really not acceptable for a motorcycle. Besides being challenging in adding water, the movement and possible tipping-over of a motorcycle would not be good for flooded batteries.

Sealed lead-acid batteries (VRLA) would also be fine, as would gels. However, neither of those can crank the power as well as an AGM can, which is what gives the cycle good acceleration. Lithium batteries are excellent for weight, capacity, and power, but are currently only for those with higher budgets. If you use lithium batteries, everything else about the project is the same, except for a different battery charger and a battery management system.

Figuring Range
Going back to some simple math, we can get an estimate of motorcycle range. I have four batteries, each of which is 12 volts, but they are wired up in one series string of all four of them, so it's really 48V in total.
The batteries are rated at 55Ah.
So, in theory, 48V x 55AH = 2640 watt-hours capacity. 100 watt-hours per mile is a typical ball-park number for energy consumption per mile on an electric motorcycle. (Of course that does vary by weather, speed, riding style, etc.) But this is just a rough estimate.
2640/100 = 26.4miles
Just a real rough estimate, but it's good enough to say "Will this vehicle meet my needs? Will it perform the way I want it too?"
In this case, yes. I only live a couple miles outside town, and the next town is ten miles away. I can use this cycle to drive all over locally, and head to the next town over and back on one charge.

In real-world driving tests, the single-charge range of the cycle came to 23 miles if I drove full-tilt, and 32 if I was doing easy acceleration and in the city 25 mph zones.

Mock-ups and CAD
Lead batteries are NOT light. It helps to make a mock-up from foam or cardboard, so that you have a LIGHTWEIGHT, easy-to-handle version of the battery to experiment with. I like to think of this as the poor-man's C.A.D.

If you are into computer design, there are many great programs out there to help you create 3D images and think in three-dimensional space. Google Sketchup seems to be getting fairly popular. Still, you really can't beat an actual, physical object in your hands. I just prefer something that weighs less than lead.

In my earliest version of the cycle, I had three batteries in it. Then I moved up to four (for more range and higher top-speed.) I was never sure how to fit four inside the frame in a way that fit well and looked good. By using cardboard mock-ups, I was able to experiment with various arrangements of batteries until I found one that I liked. In this case, the fact that I could mount these batteries turned on end allowed me to come up with a configuration that I liked.

Once the size and number of batteries are decided on, they need to be physically mounted inside the motorcycle, and solidly connected to the frame.

itscasper2 years ago
The Optima Yellow battery specifications state good for 300+ discharge/recharge cycles. Does this mean you potentially have to replace your four batteries once a year for a daily driver? Even every two years seems a steep price. Do the batteries degrade slowly over time? I'm very inspired by your instructable!
bennelson (author)  itscasper2 years ago
I've had my Optima Yellowtops for 5 years now. Still working great.

If you don't "dig too deep" in discharging, batteries last much longer. My average trip is 10 miles, so I'm typically discharging the batteries only about a third of the way.

I do sort of baby my batteries, but they WERE the most expensive part of the entire project. By taking good care of them, and always recharging them right away, they have been great!

As far as lead-acid batteries go, I don't think I could be happier.
i have a old panhead frame that i accuired from somewhere that i am thinking about making a ebike from it but i need to 55 miles round trip
bennelson (author)  thelurchmanfl3 years ago
Lithium batteries are where it's at if you need a range greater than 50 miles. Lead-acid works fairly well for anything less than that.
wouldnt that require a special charger
how would i make the battery pack out of a whole mess of aa type like the tesla roadster
and would this charger work
bennelson (author)  thelurchmanfl3 years ago
Making a battery pack from cells that small sounds like a lot of work!

Remember, you need to have enough cells in series to get to the voltage you want, and enough cells in parallel to get the capacity that you want.

I haven't heard of anyone building projects with AA cells. There are a few projects that people have built from cells pulled out of DeWalt lithium cordless drill packs. Those are more like C or D cells.

That charger is the right chemistry and voltage, but it may too low amperage. My battery pack is 55AH at 48V. If the pack is run half-way down (23AH) and you recharge it at a rate of only 2 amps, that's going to take 12 hours to recharge, and a fully discharged pack might take a full 24 hours!
bennelson (author)  thelurchmanfl3 years ago
Lithium batteries with either use a different charger, or at least a high quality one that is programmed for lithium. Lithium batteries also typically need a battery-management-system.
are there batteries with higher than 55 amps that i could use
bennelson (author)  thelurchmanfl3 years ago
Sure, batteries are available in a number of capacities. The next size up is right around 100AH.

For my project, they wouldn't have fit inside the unmodified motorcycle frame, but would be great for a "chopper" or custom frame.
Untold3 years ago
Hello again, a battery question this time: would you recommend batteries advertised as "deep cycle"? The reason I ask is that some automotive starter batteries are not designed to be discharged all (or most) of the way, as that damages them (the AH rating is only part of the story). But, leisure batteries are sometimes advertised as deep cycle so you can run them low without fear of damage. I think this applies mostly to lead acid... Are the AGMs free of this potential problem?
bennelson (author)  Untold3 years ago
Yes, you want to use batteries listed as at least DEEP-CYCLE.
STARTING batteries are NOT appropriate for powering an electric vehicle.
deepsea53 years ago
Outstanding article! Battery question: would the Optima Blue Top batteries give greater range than the Yellow Top batteries?
bennelson (author)  deepsea53 years ago
I've heard that the Optima Blue tops are internally identical to the Yellow Tops. They just have different posts on them and are a different market. Internal chemistry is exactly the same.