The magic of caring for your electric bicycle batteries

Originally published at: The magic of caring for your electric bicycle batteries | Boing Boing


Ohhh, magic!

Happy Rainbow GIF by Morphin

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The fatal flaw of most current ebikes. Standards will emerge.


The current fleet of ebike manufacturers is largely flying by night.


Bolton’s folding e-bike looks nifty, but I’m not sure if I have that big of a wallet.

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these e-bike makers should be tapping into the battery platforms of cordless tools and outdoor power equipment. These tool makers are at the cutting edge of affordable battery technology. This would hook them up to a product that was widely available and under constant development and improvement. DeWalt Flexvolt 60v, Makita XGT 40v, or EGO 56v platforms would all rock for an bike.


This video is full of fluff and nonsense. The first piece of useful info comes at 2:40.

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Most ebike batteries are between 36 and 72 volts, but unlike tool batteries which have all their cells in series, they have many of the cells in parallel too. A quick search shows from 3 to 8 groups of batteries in parallel. So that means using 3 to 8 tool batteries for a bike.

And you can’t just plug a bunch of tool batteries together on an evike- the batteries need to be well matched in terms of voltage, capacity, and charge level.

That’s not to say that tool batteries can’t be used to power an ebike, but it’s not straightforward either. By the time an ebike manufacturer has solved how to bundle a bunch of tool batteries together, it may as well have just made its own battery pack.


What’s wrong with extension cords?


I’m willing to bet these custom battery packs can all be rebuilt. There are services that do this for other applications. All these “custom” battery packs are almost all 18650 cells spot-welded together inside. With the right equipment you can test and replace cells and make the pack good for another several years. Companies exist to do this for your electric car battery, for example, and DIYers do it with their tool batteries.


Another option - subject to having sufficient braking capacity - would be to electrify an existing bike. There are a variety of hub and pedal motors out there that can work with any sufficient power source.

If you’re buying a new one, bike shops that specialize in custom-building are another way to go, if you’d prefer to let someone else do the work.

Speaking of battery care, can you charge your bike at the same charging stations as your electric car? Now, that would be something.

Do electric wheelchairs and scooters have the same battery issues? Do bikes require that the battery be a lot smaller?

Aren’t these batteries somewhat dangerous to work with in bulk? Otherwise, it seems like e-bike battery rebuilding would make a nice side gig for a well equipped home workshop.

I understand what you are saying, but first off - tool batteries often have cell groups in parallel, just as you are describing.

18v(20v) tools are based on 5 cell groups. 1.5-3AH packs are typically 1 group of 5 cells, 3AH and up are typically 10 cells in two groups of 5.

But 18v is for smaller hand tools. You have to look at OPE systems for more energy.

36v(40v) tools are based on 10 cell groups, and again higher AH packs use multiple groups of cells.

And so on for higher voltage tool batteries.

So the questions is not whether or not there are groups of cells in parallel, but rather what is the energy potential of the batteries typically used in an ebike.

For instance the EGO 56v(50.4v) packs use groups of 14 cell groups in parallel. Their largest capacity pack is 10ah and may have 3 or 4 cell groups in parallel. That may or may not be sufficient for an ebike’s power draw. I suspect it would be.

I’m not grasping at straws here. There are people doing this with their bikes, and you can find plug adapters and frame mounts for some of the large format batteries.


A lot less dangerous than gasoline, but people work around that in home shops all the time. Like anything else, you just have to know the safety procedures for them. People are scared of them because they are new, but we have plenty of dangerous things in our lives that we don’t think twice about because we’re used to them.


LION batteries are known to catch fire! But the power management of these kind of batteries is pretty well known - that’s why you don’t worry about walking around with one in your pocket. Power management manages the draw not the battery, the temperature of the cells, and the power level - often he control software does not let the cells get near empty, so that the cells are not damaged and the life of the overall power pack is extended.

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And some power tools (e.g. some ryobi lawn mowers) do take two smaller 18V battery packs and use them in parallel.

I’d be more worried about building the battery than using it. If you’ve got (say) 70 individual cells in 5 parallel groups of 14, that’s up to 100A @ 50 or 60 volts (if I have my math right). Seems like a mistake at the wrong moment could be… spectacular.

Like this?

Suddenly my EGO chain saw became a lot sexier.