Use Your Cordless Power Tool Batteries To Power Your Ebike : What Could Possibly Go Wrong?

This article has been a long time coming, but first a little history. My wife and I have 2 houses, hers is 1.2 miles from the road up a 900 ft hill and has an off-grid solar system. She is also Chemically Sensitive so we don’t really have anything that runs with gasoline except our cars. Even the generator that we use in the dead of winter is converted for use with propane so we don’t have to deal with the hassle of gasoline. The lawn has a mind of its own (it’s not really a lawn, more like 600 acres of goldenrod) and we decided for our wedding reception we wanted to actually have a lawn for our guests. On her own volition without consulting the battery expert she went out and bought a 40v Electric cordless lawnmower (it was probably only 36v and they were just liars). 40v on a lawnmower was a joke your boss tells you that isn’t really that funny but you still have to laugh, so after a few attempts to knock down the overgrown weeds we just took it back. The next purchase was a much more expensive $500 EGO 56v cordless lawnmower which turned out to be all kinds of awesome. We quickly fell in love.

lawn

The mower was powerful enough to knock down most everything (including 3ft high goldenrod) and for the most part, the design was very solid. The 4Ah battery pack ran for about 30 minutes of hardcore mowing, but it also recharged in about 20 minutes and worked very well with our PV system as long as it was pretty sunny. This article is not a review for an overpriced cordless lawnmower that you will never buy. Instead, this article talks about a very smart way to buy good lithium batteries with a built-in BMS and a decent warranty from your local hardware store, and then mount and use them on your high-power ebikes. Fasten your seatbelts because it’s going to be a hell of a ride.

A 4Ah Ego battery runs about $199 at any Home Depot store

A 4Ah Ego battery runs about $199 at any Home Depot store, Its a better deal if you buy it as a Chainsaw or Lawn Mower package.

I recently destroyed $800 worth of 6v Lead Acid Golf Cart Batteries from my wife’s solar system my setting them to equalize for 2 hours right before we left for 3 days to hike in the Catskills with visiting in-laws from Denmark. When we returned to the house it was full of smoke and the battery box was over 200 degrees and there was battery acid everywhere and the batteries were squealing and bubbling like crazy. So I donned an old Spinach container as a face shield and threw on some chemical gloves and carefully disconnected the batteries and carried them outside while trying not to get battery acid all over me. I did what any loving, supportive partner would do and agreed to pay for half of the replacement cost of the new cells (which will be closer to $1500) then I secretly sneaked away with her $500 lawn mower battery and went to my house for the weekend to extensively test them with my ebike.

Moral of the story : Don’t marry me if you want your batteries to live a long full life.

In the past if you wanted a small lithium pack that would have <5Ah of power and still produce 25Amps or more of continuous power then you either had to build your own 2P pack with a BMS out of 25R 18650 cells or another high current cell or risk using Hobby King Lipos. I pretty much rip on HK Lipos with every article I write and I assure you this one will be no different. HK Lipo’s suck and they are not worth wasting your time and energy with. Building your own 25R 14S2P pack from scratch is a time-consuming, expensive and potentially dangerous proposition. With the new bunch of high power tools on the market like cordless lawn mowers and chainsaws there are reputable companies that are producing these high power packs for cheap and selling them right down the street at your local Building Supply store. Some of these batteries are way better than others, and right now the Ego packs seem to be the best.

You can a fast charger (left) or slow charger (right) and 56v batteries in a variety of different sizes\weights and power capacities.

You can a fast charger (left) or slow charger (right) and 56v batteries in a variety of different sizes\weights and power capacities (2.0, 2.5, 4.0 ,5.0 & 7.0 Ah).

When is 56 volts not 56 volts? When it’s 52 volts

Another marketing misnomer is calling these packs 56v packs when really the rest of the battery industry would call them 50v, 51v or 52v packs, which is closer to the nominal rating of these cells. They are referring to peak volts fresh off the charger which is a hair over 57v, so you probably couldn’t actually sue them, but it sure is confusing. In any case, almost all the companies that make power tools are advertising their 14S packs as 56v so there you go. If you don’t like it then you should write a letter to some politician somewhere that they will almost certainly ignore (it’s their job to ignore you).

The battery and charger together are pretty heavy. The quick charger is even heavier.

The battery and slow charger together are pretty heavy. The quick charger is even heavier (4lbs 4oz but not shown).

There were two ways I tested this battery, one with a modified charger (which was heavy) then I took the charger apart and just used the connector piece. I bought a used slow charger for $20 on eBay shipped. I think there are a bunch of them out there that were floor demos or something because the seller I bought from had 10 of them. I took the charger apart using a security keyed Torx (the ones with the dimples on them). Then I cut the leads to the positive and negative and soldered some wire and some Anderson 45 Amp Powerpole connectors to them. I covered the junctions with heat shrink tubing then carved out a tiny notch on the case. I wrapped the two wires with duct tape, put a small zip tie on there as tight as I could then tucked the zip tie inside the case to work as a kind of strain relief so the cable would not get ripped out.

solder

Just a little snip and solder. This took me about 10 minutes to do.

I tried this configuration and it worked pretty well, although it seems silly to ride around with an extra 3 lb charger that you don’t really need. I took the charger apart again and then with two screws on the top I removed just the conductors to the battery. You can slide these conductors into the battery and they stay pretty well situated even when bouncing around in a backpack. The weight for just the connector was pretty nominal.

This ziptie will end up inside the case as a strain relief with the case biting down on the duct tape to protect the wire insulation.

This zip tie will end up inside the case as a strain relief with the case biting down on the duct tape to protect the wire insulation

This battery pack did much better in the woods than I expected it to. I tested it pretty extensively with the BBS02 and the BBSHD without issues. The BMS can do 30 amp bursts but seems happiest running at 15-20 Amps. At these power levels, the pack does not even get warm. When the battery gets run down it will intermittently stop and start so it seems the low voltage cutoff on these packs is set very, very low. According to the marking for these batteries, they also are surrounded by a blanket of phase-changing material that will convert from a solid to a liquid if the batteries get too hot. I’m sure you remember from your physics class that going through a phase change like this absorbs a tremendous amount of energy from the surroundings, so this is the way they are able run these cells very hard, and still not worry about them overheating.

Using a phase change battery wrap is an ingenious way to capture excess heat

Using a phase change battery wrap is an ingenious way to capture excess heat

The BMS on the Ego packs is potted so it is completely waterproof, but the batteries themselves are well ventilated and the Ego packs are not really designed to be waterproof. The marketing video linked to below mentions someone leaving this pack outside for the whole winter under 7 feet of snow.

“See honey, there are people who abuse batteries worse than I do in this world. At least you’re not married to him.”

Personally, I would keep them in a waterproof bag or a backpack if you’re going to be riding in the rain or snow. Keep in mind I was testing with a 4Ah pack so you might find that the 2Ah pack does not produce as much power. I cannot find any specs on the packs rated output or the cells that they are using, but if I had to guess I would say the 2Ah pack is 14S1P 20R cells, the 4Ah pack is 14S2P 20R cells, the 5Ah pack is 14S2P 25R cells, and the 7.5Ah pack is 14S3P 25R cells. The 20R and 25R are incredibly reliable and widely used in the power tool industry for several years. They don’t pack the capacity of the newer 2016 cells like the 3500Mah GA cells that I’m crazy about, but they can put out 20Amps all day long without breaking a sweat. These older cells are also dirt cheap in quantity, and Ego is probably getting them for around $3 a cell wholesale.

light

This shows the pack\charger combo. When you press the button it lights up like some kind of crazy killer robot. The cake is a lie.

It is pretty cool to think that you can just buy a battery at Home Depot then throw your 3 lb battery into a backpack and get about 40 minutes of pedal-assist riding out of it. For a lot of people who just want to bang around town with a small ebike, the Ego packs might make a lot of sense. There are other people like Echo who are also creating 14S 56v packs that are quite frankly not engineered even close to what these Ego packs are. For an annoying Ego marketing video click here and for an independent 20 minute 56v Echo vs Ego pack teardown here. The Ego pack has a 3-year manufacturer warranty which is pretty much unheard of in the industry. That being said, if you buy an Ego pack and hook it up to your ebike, then it will certainly void the warranty.

The best way to use this pack is with the conductors wedged in the slots

The best way to use this pack is with the conductors just wedged into the slots

Should you spring for an Ego battery pack? In all honesty, if you had asked me yesterday I would have said ‘yeah go for it’ but just today I just ordered a newly released 6Ah 14S2P 30Q pack that only weighs 3.3lbs from Lunacycle for a scant $319 right here. At that weight, you will not find any 18650 pack that even comes close that will be able to do 30Amps continuous and has 6Ah of range. My large 21Ah 7P 30Q pack (reviewed here) does not even get warm pulling 50 Amps continuous so I’m certain that the 2P 3lb pack from Luna will be fine at 30Amps and less (and it has a thermal cutoff just in case). The pack is so small that it will literally fit in your pocket with room to spare. The same could not be said of any of the Ego packs, even the 2Ah one which is pretty huge. I will be doing a review of this new Luna Mighty Mini 3lb pack as soon as it arrives so stay tuned, suckers.

The industry marches on as our old packs are quickly made obsolete.

Thanks to Ron\Spinningmagnets for the terrible idea to write this article. Ron both looks and acts like my Jedi ebike Master, but instead of saying wise things like Obi-Wan does, he is more like “Hey Karl, don’t be such a dick and maybe people will like you more”.

Thank you, master Yoda.

It’s not easy being green.

Ride On.

43 thoughts on “Use Your Cordless Power Tool Batteries To Power Your Ebike : What Could Possibly Go Wrong?

  1. I bought one after getting the intro email. A lot of DIY builds don’t have an obvious place to put a battery, especially a large one. I’ve been using HK Lipos in a handlebar bag, small and light, on a step through. I’d be happy to retire those packs, but the Lipos have worked.

    These packs would also help to lower the entry point for new builders. The Smart Pie is a nice motor for around $300. Something like the SP and one of these packs plus a used bike? You would own a swell motor and a good battery.

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  2. Another great article, Karl! A few years ago, the only way to get high-amp cells was to gut cordless tools, so I did some reading on them. My first ebike was a DIY friction drive using RC model components, so they operate well on lower voltages. Oddly, the 28V packs used higher-amp cells compared to the 36V cordless tools. If I had begun making and selling friction drives to college students, I was going to use Milwaukee brand 28V battery packs, so I wouldn’t have 18-year olds burning down their fraternity dorms with LiPo. If I was designing a power-board today, I’d use those 28V packs and pneumatic tires…

    Liked by 1 person

    • Thanks Obi-Wan. Yeah nothing beats those 20R & 25R’s for high output, cost and safety. The market drives the industry, the ebike stuff is just fringe and sometimes it feels like we’re all just along for the ride.

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  3. I’ve had an EGO for a couple of years and have wondered about using the battery as a range extender. I have a Catrike based velomobile with a 2000W MAC and a KW-hr of LiFePO4. I think my two bricks weigh ~20 lbs. I could toss my EGO battery in the saddle bags and extend the range 40%.

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  4. Funny how we don’t really have what we want/need but always seeking what we can use and improvise.
    My 2 stroke 30yo lawnmower I had since a kid with barely any maintenance was getting to recon time. Wife always wanted to mow lawn and kid across the road was doing their lawn with electric like a cordless vacuum. I saw the 52-56V EGO used on a cruiser ebike (fugly, bulky with charge cradle used as the on-bike dock), we only had 4Ah packs available, so got that and the blower with 2Ah pack, with ebike use in back of mind.

    Really nice user friendly quality as you’ve shown in this blog. Too bulky for too low 4Ah capacity for ebike I thought, but the 7.5Ah sounds good, and the shared use mower/blower/ebike is the kind of quality battery sharing to help justify long term care and use.

    In the interim for suitable range the 16Ah 6S HK LiPo in a 12S pair fit in a lunchbox that fits in frame bag for similar size to the Ego 4Ah, but I can run only 50% discharge, 80-90% peak charge for longer life for most recreational use. I can use full capacity with 2 pair for 32Ah in duty standby for long range. Also provided auxiliary range to my Bosch system, and individually the 6S is a double capacity of the GoE OnWheel friction drive about to deliver from Kickstarter… So these 16Ah are good capacity and versatile across multiple ebike drives. Of the 4 cells I can use 3 for a 72V 16Ah pack in a direct drive hub motor kit as well.
    A DIY magnetic connector to the Ego battery spades would be handy. I hope the Ego products continue and we get the battery filter down.

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  5. I was just at Home Depot and then checked out their and EGO’s websites. They tend to only carry the package deals in house. If you want a tool w/o battery and charger or just a battery, you have to order online.

    Does anyone have knowledge of the dimensions of the 7.5 A-hr unit?

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  6. Is there a picture of the bike this battery powers? Mortorcycle, airplane, whatever… let’s fire it up and see what she’ll do.

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  7. I would have never have thought of doing this.

    Since I was in the market for a battery, I went for the 7.5ah pack, its a really solid high discharge pack. I’m very impressed with it.

    Thanks for the top tip Karl!

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  8. Pingback: The Most Power You’ll Ever Be Able To Fit In Your Pocket : 6Ah 3.3 lb 30Q Luna Mighty Mini Cube Pack Reviewed | ElectricBike-Blog.com

  9. Thanks Karl! Had just finished modifying a battery box from an ego mower into a battery mount, when my lunagizer went down and I had no way to charge my shark pack. (support has requested a replacement, thanks Louis!) But because of your inspiration I am still motoing! Getting about 4 real good miles, and another 1 1/2 weak miles from a 2ah battery. Got a charger, 3-2ah batts and the batt box for $180 delivered! Not an ideal solution to a spare battery, but it works and was cheap! Oh yea, the reason I went this route is I run a lawn care business and were switching to battery electric on all our small engine machines. Guess which manufacturer we use! Hehehe! Life is grand!

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    • Is there anyway you can show pics of your setup as I too have 1 7.5ah one 4.5 and 3 2ah Ego batteries and am wondering if I should cannibalize either one of the 2 blowers I have or one of the 3 slow chargers in order to make a mount/connecting solution! email me at dpromano76@gmail.com

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  10. So I’d like to use the Ego 4Ah Battery with this Front Wheel Hub Electric kit
    – is the 48volt hub motor & controller close enough to the 50-52V actual provided from that battery?
    – Do I need any special adapters or converters (other than the charger connector piece/prongs)?
    – if the battery is 4Ah, and I assume 20wh/mile is typical, How many miles will this last on it’s own?

    http://www.amazon.com/Generic-Motorize-Electric-Bicycle-Conversion/dp/8805001546
    Generic Add-on Motorize Bike 48v 1000w 26 Inch Front Wheel Electric Bicycle Motor Conversion Kit
    by Generic
    4 out of 5 stars 52 customer reviews | 103 answered questions
    Price: $218.33 & FREE Shipping

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    • It might work, might not. Buy the kit and hook it up to a battery that reads 59v or so on a meter and see if it works before you buy the ego battery. In my experience there is a 90% chance it will work.

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  11. Ive just got the E-GO lawn motor and its awesome! I was able to mow 4000sqft and still have a green charge amount indicated! So I bought the 7.5ah today and 2 blowers that came with 2ah batteries and slow chargers and also have a 12 inch trimmer on order! I already have a couple stump-jumpers,KHS dual suspension, and a off road tandem that are all potential candidates for electrifying , I either want to go with a 1000watt rear hub or a bafang/8fun 1000w mid drive. I have a 8.1mile commute which I do now on my KHS road bike. Now how do I hook them up? do I cannibalize one of the blowers? for its clip in battery port?

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    • No it will not. You need a 52V battery for that kit, a 56v battery might also work. Power tools claim the peak charged capacity and the ebike world uses nominal battery. A 48v ebike kit means will need a 52v Power tool battery.

      It’s confusing and stupid, but the power tool pack makers want to make their packs LOOK more powerful than they really are.

      Karl

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  12. What would you recommend for that battery? I’ve got a bunch of these GreenWorks 40V batteries and was hoping to hook one up to my bike

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  13. For several years these have been teasing me as this millenias potential “D” cell.

    The ‘waxy’ wrap etc. you report is why though however it is not it. A general purpose rechargable battery is still out of reach.

    The Washington Post this year i think reported on a mandatory leaf blow silencing effort in the beltway and noted the commercial battery price which was promissing! I have also been attuned to the forklift market as we folks like them live on ultralow voltages compared to cars duh.

    Recently phase change and compression storage system’s have begged the question we raise- which is if watthours not kwh’s are needed does ignorance of physics prove almost essential to disrupt?

    Yes and no! If by ignorance one means experience over dogma then absolutely! You don’t need a loan to buy dry ice to sprint to work with, and warm the globe little on a road bike versus any car even if coal powered steam versus hydrogen fuel cell. A person gets commuted for x amount of damage.

    So strapping several leaf blowers to your rear wheel cargo rack does not void there commercial at least use warranty per se right? Next year they should be blue tooth controllable fully.

    Presently it is legal to sell, buy, and use bikes that have us be dead ducks in left turn lanes should we see a car barrelling down on us- DESPITE compresssed air energy storage making a seat post capable of raising us out of collision reach Height an ample time an easy cheap defense mechanism. Synergy has yet to so occur.

    The electric car market is ruining a once in history opportunity to make people scaled vehicles regain road use.

    We do not have to concede or worse defeat outright ourselves.

    Moble energy storage needs to be traded like dirt only recently has been. Commodify it or in a decade cars will still be legal and act like they are as immortal as they have so far duped most into assuming.

    Human power prejudices are the greatest threat to life on earth.

    What home depot carries is all important. No entity will be condemned more historically then those like Optibike who should of not merely could of risked more to destroy the car market.

    Tesla if it was not pure evil could commodify the under hundred volt low KWH market, could pay it forward with same day warranty replacement etc.

    Mobility remain where cell phones where a decade ago- no standard charging port, cars being flipped two or three times in a year for there rebate etc. Assistance while we have more spent on oppressing us!

    We see in the nailing market internal combustion remains, yet no hydrogen combustion bike has ever been mentioned even as a concept to me.

    We have the right to augment human power with whatever can be frozen, burnt, ‘energised’.

    Nobody has ever worked on designing ridable machines rationally.

    This must change. Systems to accelerate, to offset rolling etc. Resistance, to anticipate or avoid or ridiculously suddenly stop should not have any parts in common, the price to unify such features has been planetary extinction because cars have Always been unaffordable to do at all right.

    Bikes now can be engineered correctly and even used publically STILL, but not for much longer.

    If it is not ALREADY too late any FURTHER delay WILL guarantee it never happens.

    We can kill car sized contraptions if we resist evil, if we demand access to off the shelf technology not be so taxed, deterred,obscurred, as is practically rejoiced in without exception.

    Thanks for recognizing the potential disruption of even illusory free market in human muscular drive evolution . . . I salute your losses.

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  14. Thanks I enjoyed the article very much right now my only bike is a 3-speed Brompton I’m hoping to find either a hub motor or a Friction Motor that I can run with my drill batteries thanks for any ideas also I have looked at the Grin kits are they a reliable choice?

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  15. Hello, I posted to your build thread James and thought I might do so here as well. I have a large assortment of the EGO tools and batteries and just have done an Electra Townie build with the Bafang BBS02 and using my EGO batteries.

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    • By the way. On my build I took 1 of my slow chargers and cut away everything but the center part that the battery slides onto and mounted that to the rear rack on the bike. I can slide on any one of my EGO Batteries onto the mount and away we go. I still wrap a single bungie cord across the battery for safety since the slow charger fits snugly but it is not a locking connection like on the tools.

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  16. Hi Charlie, I just saw your post on ES. I added an idea for a low frame mounted battery box that would allow shorter battery cable and freeing up the rear rack, or removing it altogether to emphasise the nice frame aesthetics.

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  17. Pingback: It's possible to use a cordless tool battery on an ebike | ELECTRICBIKE.COM

  18. Can anyone recommend any type of nickel or copper strip/conductor that could be used to insert into an EGO battery? What are the two middle leads for? Besides the positive and negative lead on the right and the left, mine has a “T” lead as well as a “Ohm” lead in the middle. Do I need to do anything with these? Thanks in advance.

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  19. Hey Karl,
    I built an ebike couple months ago with the Ego 56v arc lith, based on your blog. I love it! It’s fast, dependable and a lot of fun. My only issue is with charging. I’ve returned twice and I’m currently as of this morning in the same position as the last two times. The first initial charge out the Ego box is fine and sometimes up to 3 to 5 charges after riding. The problem occurs when I go to plug the battery in “when it fails” “the charger that is” the lights both the green and red will blink once and it’s done.?.?. I’ve tried looking on the charger for a reset, I swing the battery longer for total discharge, unplugging for ahile, keeping it plugged in for time. Nothing no response what’s so ever no blinking lights nothing. I have the Ego battery wired like you said “using another battery chargers internal 4 prong clip wired to my bike. Ebike has a black and red wire witch I connected to the 4 prong clip 3 “wires not including the red” to the black and then red to red. Bike works great no issues. When I go to plug the discharged battery into the charger ” not modified ” it does this?.?..?. My question do I have to do something “wire” the inside of the charger different is the bike changing the battery in some way? Am I not plugging or using The charger correctly? I do take the charger on trips with me some times if it’s a long journey. The first time i thought maybe the charger got shook up and broke internally. But the exact same thing happened the last time. Please help!

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