An electric mountain bike is a great thing, but sadly they do not go very far. Mine had a maximum 15 mile range, on a good day and with flat ground. I got the Curry electic mountain bike online from Walmart for about $350, which is very cheap for an electric bike. But I was often left stranded somewhere trying to pedal an 80 pound bike back home on my own power. That is no easy job due to hills and rough roads.

The new battery packs for these bikes are very expensive, so that was not an option. So I decided to extend the range of my bike by adding more lead acid batteries. I wanted to keep the bike original, so the only thing that was modified was the original battery pack.

 

 

Here is how you can make your own electric bike battery pack:

First you need to determine the voltage of your original electric bike battery pack. Most are either 24 or 36 volt, but some may be 12 volt or 48 volt. Lead acid batteries normally come in 12 volts, so you will need to wire up batteries in series in order to get the correct voltage for your bike.

My bike battery pack is 24 volts, so I needed two 12 volt batteries. I had a pair of 12 volt, 10 Amp Hour batteries laying around so I used them. You can also use car batteries or lawn mower batteries if you have them around.

I did not want to modify my original electric bike in any way, so I found a way to mount new batteries to the original bike rack over the rear wheel. I went to the hardware store and found a mailbox post mount for a few dollars. This was the perfect size for my battery mount. But it was a bit flexible and that was undesirable so I attached two metal bars to it for strength. Then I simply used plastic zip ties to hold the batteries in place and a piece of scrap wood to keep them from rubbing together. In the bottom of the first image you can see little bits of foam to protect the batteries from rubbing on the metal edges as well. I added a wire between the two batteries from plus of one to the minus of the other to make a total of 24 volts.

Now I had a removable battery pack. Next it is time to mount it to the bike.

In the second photo below, you can see that I modified my original battery pack. I opened it up and soldered two wires on the inside. One to the 24 volt positive lead and one to the 24 volt negative lead. Then I mounted two banana type jacks to the outside of my battery box and soldered the two new wires to the inside of the jacks and closed the battery box. Measure the two new connections with a volt meter to make sure you have the right connections and that you have power to them.

 

 

Make The New Battery Pack

Wiring To Original Bike Batteries

Mount Homemade Battery Pack To Your Bike

Homemade Bike Battery Pack Finished

Now all that remains is to mount the battery pack to the electric bike. Again I did not want to modify my original bike at all, so I found a way to fasten my new homemade battery pack to the bike. I used some J shape bolts with a long leg on one end and a short curve on the other. These bolts go underneath the original bike luggage rack, up through the new battery mount and then are held in place with wing nuts for fast removal. You can hover the mouse over an image for a larger view.

In the third and fouth photos you can see that the new homemade battery pack is mounted securely to my electric mountain bike.

Now for the real test. A ride in the hilly area where I live. There are very steep hills that take forever to climb around my home. Before I could hardly get more than about 5 - 7 miles away without running out of power. Now I can go about 10 - 20 miles with ease and still have some power when I get back home.

Below is a photo I took about 10 miles away from home at a park. You can clearly see the wiring hooking up the new battery pack to the original electric bike battery pack.

You can use whatever batteries you have laying around. Alarm type batteries, UPS batteries, lawn mower batteries, golf cart batteries or car batteries will work to extend the range of your electric bike. Just be sure that you do not exceed the weight limits of your luggage rack.

If you have a bike trailer laying around, you can even put some heavy duty marine or deep cycle batteries in the bike trailer with wires going to your original bike wiring. This will greatly extend the mileage of your electric bike. To keep your batteries topped up and lasting for many years, use the Homemade Battery Restorer once in a while to break up sulfation on the plates.

Have fun!

Feel free to ask any questions or get help with your project on our Support Forum.

About the Author

Troy Reid

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