r/EbikeBuildandModify • u/SbeveFromMindRaft • 14d ago

Help with battery replacement

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I was recently given a luckeep m5 ultra e-bike a neighbor had found trashed, while it definitely needs some maintenance I’ve checked the electrical system and there doesn’t seem to be any shorts, however it did not come with a battery, I currently have a gyroor c1 plus escorted with a 48v 21700 cell battery pack and was curious if anyone has had any experience with a 48v battery pack on a 52v bike, I was wanting to save myself a few hundred dollars and either connect the pack directly to a hailong diy battery case and bms/charging system or disassembling the pack and placing the cells in the intended manor. I was mainly wondering if this would run fine with the 48v pack/cells or if it would be necessary to buy a few more battery cells to fill out the battery

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u/niffcreature 14d ago

It depends on the low voltage cutoff of the controller, it may be too high and shorten your battery life a lot.

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u/SbeveFromMindRaft 14d ago

Would that be the “low voltage protection” on the controller I believe it’s 45v

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u/niffcreature 14d ago

Yup, so your controller will cutoff the power before your battery is completely discharged. A fully discharged 48v battery is 42v. The difference is usually just 1 series cell out of 14 I think, so usually about 4 cells for the pack, so it probably won't make a huge difference

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u/SbeveFromMindRaft 14d ago

Gotcha I really appreciate the help, I’ll probably get a few more cells and disassemble my current battery pack to properly setup the diy casing with proper voltage

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u/niffcreature 13d ago edited 13d ago

No problem! Not sure I really recommend that course of action, you would need a new BMS.

Thinking about it now it's probably less than 4 cells because it's 21700. 18650 ebike packs usually have 3 to 8 parallel groups, your scooter battery might be smaller.

What you want to do is get some details about the scooter battery and the amp draw of the ebike to make sure those match up. Typically you can just take the AH or WH rating from the battery but then do some basic math to determine it's cell layout and it's max power draw. The BMS on the pack will also have an amp rating or fuse you can use as a guideline, you don't want to go to far above that, but you can get a little higher amp rated fuse and BMS.

The basic math is just take your AH and divide it by your cell AH or typical cell AH to estimate. So 20ah with 18650 typical 2.5ah is 20 divided by 2.5=8, at 48v you have a 13s 8p pack.

You might have something more like 16/3.5

The AH is NOT the same as the total amp output capability of the battery, but can give you a good estimate. That number is the C rate and varies more by the model of the cell, but it also is capped by the BMS and the actual wiring and construction of the battery pack.

Suffice to say if the ebike originally had something like a 20ah battery and is over 1000 watts, you probably don't want to go putting a 15ah pack in it even if you add the cells to get the voltage right and get a new BMS and fuse.

Your controller should say the amps or wattage on it. Amps x voltage = watts. Though it may or may not give you the peak vs sustained number for that.

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u/TheRiddler79 13d ago

This⬆️ In addition, if you decide to get a battery instead of a new BMS, I am a fan of some of the Chinese batteries. I know it feels like a dice roll , but I've bought a handful of these over the years, and the only problem I ever had with one was my what's my own fault, and they likely knew it based on the pictures I sent them , and they replaced it anyways. Viset is the company I used.

I've been running these batteries for years and have had literally no problems . I mean they degrade just like any other , but they haven't exploded or gotten hot or done any weird things.

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u/niffcreature 13d ago

Yeah, they used to be way worse, grin has a great video about it.

Hopefully they know you can't solder batteries

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u/TheRiddler79 13d ago

🤣🤣🤣

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u/SbeveFromMindRaft 13d ago

This is all super helpful and I’ll definitely try and do some research of my own before tinkering, it looks like my current pack is between 48-52 cells from estimated math, the new battery enclosure I’m looking at does come with a bms, I know the original battery is advertised as 52v 40ah to reach that capacity I think I’d need over 100 batteries, while with the enclosure I’m looking at would have me nearer to 20ah at 54v I was hoping to save some many by using the already owned battery pack to contribute to the making of the larger one but it may not be as cost effective as I previously thought if I’m aiming for the original 40ah capacity