Thanks so much for the info, that sounds great and an exciting option! I understand the warranty issue but aside from that, you don’t see any issue than with building a battery of any capacity and just making the discharge cable with an xlr connection to plug into the bike. Would I need a different cable to charge the battery or does it charge via the xlr connection like theirs? Here is one more link with a few more answered questions about their auxiliary battery if you wanted more info. Thanks again, this is really exciting, I just want to make sure I don’t fry anything

As you draw current from a battery pack, the voltage will very slowly decrease until the cells start to go flat and then the voltage will plummet. The time that the battery lasts for is directly related to its capacity, measured in amp-hours (Ah). A pack that can deliver 1 amp for 1 hour has a capacity of 1 Ah. Most ebike batteries are on the order of 10 amp-hours. Suppose your bike uses 15 amps on average and has a 10Ah pack, then you would expect it to last for – quick, mental calculation… – 40 minutes.

I figured this would be a critical step I wouldn’t want to mess up. Thanks for the advice on using the multimeter. That’s good to know as I thought I might need to open up the controller and see which wires went where on that male xlr connection which I guess would be an option too. Thanks again!

The only two ebike companies that sell LiPo to the public are Optibike and Pi-cycles, and both contain the battery in a strong metal box which makes up of the frame. The companies fire tested these enclosures and are confident that their frame are effective and safe vessels for LiPo storage.

If any one battery cell varies significantly from the others, do NOT connect it to the other cells. Paralleling two or more cells of different voltages will cause an instantaneous and massive current flow in the direction of the lower voltage cell(s). This can damage the cells and even result in fire on rare occasions. Either individually charge or discharge the cell to match the others, or more likely, just don’t use it in your pack at all. The reason for the voltage difference could have something to do with an issue in the cell, and you don’t want a bad cell in your pack.

Most of the problems occur when charging an ebike because they are unsupervised and that is when a LiPo fire can burn down a house etc. Use common sense on where you are going to charge your bike or battery pack, so that if it does burst into flames it does not take your house with you. I have a big steel barbecue grill set up in my entryway which  I charge my battery packs in  as nice safeguard.  This involved taking the battery pack out of the bike after each ride but I am OK with that:


Well, I’ve finally built a pack, which in the end turned out to be a 16s6p/7p made from recycled dead laptop batteries, charging to 67.2V and has a secondary offtake for a controller on the 13s positive (i.e. to route 16s to the FETs and 13s to the control circuit). Some of the groups were OK for 12Ah from 6 cells, others needed 7 cells; I just used what I had and as I got the laptop batteries for free, it was better for me spend the time testing them than to use 80 new cells, which would have been quite expensive.

After writing my question, I did more research on these cells regarding overcharging and over-discharging and I see where you’re coming from regarding not having connections between the parallel cell blocks to smooth out differences between individual cells. So as a permanent installation, it’s not going to work. However, I’ve had another thought, which I’ve put at the final paragraph.

Hi Sundaram, I’m not aware of many 18650 LiFePO4 cells, are you sure you are using that chemistry instead of standard lithium ion? Perhaps can you provide a little more detail about the specific cells you’re using?

Lithium aside, even Lead acid batteries can be a fire risk… including the battery used to start most automobiles. The only battery fire I have experienced myself was when a wire dropped onto a lead acid battery, shorting it, becoming white hot and burning off the insulation, scaring me out of a years growth, and being ejected from the office onto the back deck in less than 10 seconds. This experience also gave my wife a lifetime supply of snarky comments about the “big bad battery expert who set fire to a ‘safe’ battery in his office!”

Before I seal my batteries in heat shrink, I like to wrap them in a thin layer of foam for added protection. This helps keep the ends of your cells from getting dinged if the battery receives any rough treatment, which can happen accidentally in the form of a dropped battery or ebike accident. The foam also helps to dampen the vibrations that the battery will experience on the bike.

I placed the first parallel group positive side up, and the second parallel group negative side up. I laid the nickel strips on top of each of the three sets of cells, bridging the positive caps of the first parallel group with the negative terminal of the second parallel group, as shown in the picture.

LiMn/LiMnO2-Lithium Manganese Oxide. Adding manganese to the cathode made this chemistry more stable and less sensitive to individual cell balancing issues. If you were using LiFePO4, and one cell began losing its amp-hour capacity, the rest of the pack would get dragged down to the weakest cells level. Demanding high amps with one weak cell in the pack would cause the entire pack to wear out much earlier than it should have.  With LiMn, the packs just seems to stay in balance, with all the individual cells aging equally.

Connections are made with solid Nickel strips, spot welder to each cell. Each cell and each series is tested before assembly. The BMS will prevent over charging and will balance the cells after a full…

36V10Ah Li-Ion NiCoMn “Little Frog” ABS shell ebike battery pack. Included 2p10s 5Ah polymer cells, 1pcs 15A continuous discharge current BMS, 1pcs 36V2.5Amps EMC-120 Lithium Ion battery Alloy shell charger.

This is how most Asian batteries are built, since they use the same size aluminum or plastic case, but offer different sizes and capacities of batteries in the same case. I’ve used arts and craft foam, which often comes in sheets up to about 5mm thick (and I use a few layers to fill larger gaps). For MUCH larger gaps where that thin foam is less desirable, I’ve seen people use styrofoam or even that green molding foam often used in pots to hold up fake plants. That stuff is a fairly rigid though, so maybe a combination of that stuff and a layer of softer foam for cushioning would be good.

If you want to test cells from different vendors, the best thing to do is run them through a discharger, preferably a fancy graphing one, and preferably at a high current rating close to the maximum discharge rating. Fake cells are lower quality and won’t be able to provide the same capacity, and will have a larger voltage sag under higher loads.

Hi, if this is the first time you’ve heard about us, we recommend that you search “bmsbattery” or “bms battery” on Google or any other search engine to find out more about our excellent products, service and good reputation.  Time has proven that we are the best

I buy that pink cells, Samsung ICR18650-26F. The cells have 3,9V, is a little too, only one with 3,82 and the other 3,87. I want to do a pack with 4parallel and 7serie (28 cells), it is acceptable conect them? Any sugestion is welcome.

I purchased the 220v welder, which obviously was intended to run on non-US half of a phase 220v, Of course we have full single phase 220v, so could you supply me with a hint on how to wire the unit for US 220 v.

The sense wires generally connect to the positive of each cell group, but sometimes there is one more sense wire than parallel groups because the first sense wire is intended to connect to the negative of the first cell group, then all the subsequent sense wires connect to the positive of each cell group. Each BMS should be labeled on the board to show where each sense wire goes (B1-, B1+, B2+, B3+, etc…)

I’m sorry to hear about your bad experiences with AliExpress. I’ve done a lot of business there, and I’d say only around 5% of my transactions have been problematic. They have great buyer protection though and every time I’ve either gotten a full refund or had my product replaced at no cost. If you want a BMS from a source other than AliExpress or eBay, I recommend a company called BesTechPower. They make the highest quality BMS’s I’ve seen and they are the ones I use on my “top shelf” batteries. They are pricier, but you definitely get what you pay for. Just email their contact addresses and they can help you choose a BMS.

Hey Brian, good question. You can actually do regenerative braking this way, the only problem is that you won’t be using the balancing circuit part of the BMS as it will charge straight back through the discharge circuit. Theoretically this is fine, with the exception of one specific case where this could be a problem. If you charged your battery at the top of a huge hill then immediately rolled down that hill for a long time while using regenerative braking, you could actually overcharge the battery. That scenario is pretty rare though.

5. Prizes: The approximate retail value of all prizes is $1361. The prizes are: Performance E-BikeKit or Heavy Duty E-BikeKit. You are not guaranteed to win a prize and your chance of winning is dependent on the total number of eligible entries received. Actual/appraised value may differ at time of prize award. The specifics of the prize shall be solely determined by the Sponsor. No cash or other prize substitution permitted except at Sponsor’s discretion. The prize is nontransferable. Any and all prize related expenses, including without limitation any and all federal, state, and local taxes shall be the sole responsibility of the winner. No substitution of prize or transfer/assignment of prize to others or request for the cash equivalent by winners is permitted. Acceptance of prize constitutes permission for Electric Bike Technologies LLC to use winner’s name, likeness, and entry for purposes of advertising and trade without further compensation, unless prohibited by law.

Unless you’ve got a specific design need, it feels to me like the two best value at the moment for a typical E-Bike build are 36v15Ahr and 48v10Ahr. With the choice being LiNiCoMn for smaller/lighter/cheaper or LiFePo for lifespan/higher-C but a bit more heavy/bulky/expensive.

It was an interesting project to say the least, particularly how to link the Ch- and the P- from the BMS taking its B- from the 7s negative termination to the positive of the 6s group, given that there are two routes (i.e. charging and discharging), so connecting both simultaneously would override the function of the BMS.

Please do not ask us to overvolt or otherwise modify your eBike to exceed 20 mph. First off, we have yet to have a customer who has (on their own) overvolted their bike to go above 25 mph and avoided a hospital visit within their first 6 months of doing so. [redirect url=’’ sec=’7′]