Running a Cordless Electric Lawn Mower on an eBike Battery?

As many of you know, some time ago I experimentally bought a cordless electric mower. However the largest capacity battery it would accept held only 200 watt hours of energy. This was enough to get through just under half my lawn, including the strips of grass between the sidewalk and the street.

I wound up returning it because I felt for what I paid ($350) it ought to have been able to do the job on a single charge. There exist high end lithium cordless mowers like the Ego 56v that would do the entire lawn on one charge but they’re also twice as expensive, between $600 and $700 depending where you buy and when.

This is when it occurred to me that the solution to my problems was under my nose the entire time. The problem? Electric mowers are sold by power tool companies, which make their money by gouging consumers on the proprietary battery packs that lock us into using their corresponding family of power tools.

The solution? Modify your tools (mower in this case) to use a type of battery pack that has already been driven down in price as cheap as it will go by the eBike market. The wattages that ebikes need are very similar to the wattages an electric lawn mower needs, and the voltages tend to be multiples of 12.

This is because ebikes were originally powered by lead acid batteries. To maintain compatibility after the market switched over to lithium, lithium battery packs for eBikes are generally made in voltages that are a multiple of 12: 24v, 36v, 48v, 72v, etc.

This makes cordless mowers and eBike batteries a perfect match. You can pick up a 36 volt cordless mower designed around lead acid batteries used on Craigslist for perhaps $100. Since lead acid batteries are huge and bulky, the mower will have an amply large battery bay you can fit quite a sizable eBike battery into.

Alternatively, depending what type of eBike battery you already own (or can afford) you could mount it externally by drilling a pair of holes into the mower exterior and attaching the battery mounting bracket with screws, as shown below:

This would make the battery easily removable for charging, and easily swapped between your eBike and your cordless mower. Total cost of the mower, battery, extra mounting bracket and correct adapters/plugs? About $500. That’s $100-$200 less than a prebuilt, top of the line lithium cordless mower with one third the battery capacity.

I plan to do this myself when money permits. But for anybody rubbing their chin and thinking about putting this plan into action, just remember that the voltage of the battery must match the voltage the mower expects, and the battery should be able to supply the amps the mower expects as well. Really, the higher amps the battery pack can put out, the better (the mower will use only what it needs).

I wish this post was documenting the build process rather than just describing the intent. When I have money to spend on anything besides rent, utilities and food again you can look forward to a step by step build process documentation here on my blog.

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