The Ebike Battery Project

This might not be of interest to a lot of people, but it’s what I’m doing right now, so I’m blogging about it. The weather has been worse than crumby lately, so things to do indoors are in high demand.

Building a 100km battery for my ebike will certainly be a learning experience for me, and there’s no guarantee that I will succeed. I’ve never done anything like this before, although I’ve built many things. However, it has been done many times by others, so I felt it was worth a shot, since it will be the only way that I can have a battery with this kind of range.

Even though, if successful, this battery will cost me probably 1/10 of what it would cost me to buy a battery of this type, the cost is not unsubstantial to me. I expect that, when all ready to go, this whole effort will most likely cost around $200., some of it for the actual cells, and some for other pieces that will be required to use this battery, such as a proper battery charger.

You can’t charge lithium batteries with just any battery charger, it has to be a special charger. Also, lithium batteries must be balanced, unlike lead acid batteries, which will self-balance if wired in series. To achieve balancing, there are two methods being used, a balancing charger, or a Battery Management System(BMS), which is a circuit board that would be wired into the battery itself.

From my research I’ve found that there is much uncertainty about which system is best, or even if both are required. However, I’m not anywhere near that point yet, so I’ll just take this one step at a time.

I received the 15 used laptop batteries that I purchased on ebay for $42.


This is what they looked like. They are all the same types of lenovo batteries, since I had read that you should use all the same types of cells in a battery pack.

However, I had assumed that, since they were all the same type of lenovo batteries, that the cells in them would be all from the same manufacturer. I found this assumption to be untrue.


I opened the plastic casings and this is what I found. The red cells are from Sanyo, the lavender cells are from Panasonic, and the light blue cells might be older Panasonic. So, I got a mixture of cells but, as you can see, most of them are Sanyo.

From this point, I will have to take the cells apart and check them for voltage, to see which ones might be useable in my battery pack. Anything above 3 volts will be considered ‘good’ for now, anything less than 3 volts will be considered ‘questionable’, and anything less than 1 volt will be considered ‘not likely’. However, I will be testing them all at some point.


Here are the cells, which have been separated. Some are still joined together in groups of 2 or 3, since this will help with testing and pack assembly. I’ve already check them all for voltage, and the one row at the very top are below 1 volt, the next row down are above 1 volt, but less than 3 volts, and the last four rows are above 3 volts.

So, I guess I didn’t do too badly, since I expect nearly all of those in the last four rows to be good to use, and it’s quite possible that many of the cells above that can be used, but I’ll have to test them more to find out.

This is all I can do at the moment because I’m waiting for a small lithium battery charger to come on a slow boat from China. It only cost me around 2 bucks though, so I can wait. When I get this charger, which will charge two cells at a time, I will charge each cell to the working voltage of 4.2 volts, and then I will let them rest and see how well that they hold this charge.

This step will give me a better idea of which cells to use for my ebike battery pack. I will have to get a few more packs off ebay and, if I’m lucky, they will be the same red Sanyo cells, so that I will have 120 ‘good’ red Sanyo cells for my pack.

Once I have confirmed that I do have 120 good cells, I will have to make a decision on how I’m going to connect them up, both physically and electrically. I have some ideas but, like I said, one step at a time.

In this case, I’m building an ebike battery, but these cells could also be used for a lot of other purposes, such as back up power, or many LED flashlights use lithium cells like these, so it could be worth it to someone to collect old laptop batteries and harvest the cells for reuse. As you can see, many of the cells are still in fine shape, it’s usually just one or two cells in the pack that have gone bad.


2 responses to this post.

  1. Funny, I have a Lenovo Laptop!
    Keep us updated on this electronics trip and thanks.


  2. Yep, Wild_E, I also have a lenovo Thinkpad. I always used to buy Thinkpads, even back when IBM made them. They’re great laptops. That’s one of the reasons I chose the batteries from lenovo laptops. I figured, if the laptops are quality, then the batteries are probably pretty good too.

    I will be updating this project as things progress.


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