Pre-Built Battery Pack - Can it be saved?

Hey everyone (sorry about the long read, but I like to provide context)

I’ve been working on a DIY build, but ran into a small (actually… it’s gigantic) issue with the pre-built battery pack I purchased online from a vendor here in the US (it rhymes with Mboards). After having plugged it in to charge, it popped scaring the shit out of me. It appears some debris shorted the charge port, and I thought I had blown the BMS. I emailed the vendor asking whether I should send it back to him to have a look or whether I can do it myself - he never responded. I’ve seen others complain about how much of a flake this guy is and quite frankly that has been my experience as well. He has only responded back 1 time out of 3 queries I’ve had.

I opened it being careful and found that the BMS (it’s actually a 50A and not a 60A as he states) had not fried, but in fact the charging port wiring had burned up. There was a 3 stage wire reduction starting with 18AWG wire from the C- on the BMS, down to 20, and then once again down to 22 to the charge port itself in short segments very poorly soldered together, but at the very least heat shrinked (small victories, right?). Measured voltage at the BMS and all packs looks great. Easy fix - so I thought.

From a high level, looking at the pack without even having to perform any deeper inspection, it’s scary. I decided to inspect the rest of the pack. On the outside the package looks very well built, but once you open it up, it’s a cancerous nightmare that is a fire hazard waiting to happen.

  • Balance wires are brittle and sit atop of the cells with only 4 pieces of 1cm tape holding the BMS, and all balance wires in place. Over time vibration + heat generated could easily cause a short potential

  • Balance wires connected to the positive terminal using a right angle piece of nickel. The balance terminals do have heat shrink, but are sharp creating another short potential

  • The BMS sits on top of a piece of adhesive backed fish paper with one small piece of tape (~1cm in width) holding it to the battery pack

  • Now the scary part. Some of the stock wrap around each of the 30Q cells (pink wrap) is compromised BADLY. They’re torn exposing the cell body. Others look like they have been cut during the build process and never repaired. This is the worst part. I cannot believe this shit. I could have been injured badly

Safe to say I have no plans on using this battery in this state.

I’m now in the process of building a new flexible pack (purchased PCBs from Kaly, all new 100 x 30Q from Nkon, 2 x 80A HCX-D223v1 with eswitch BMS, looking at the SUNKKO 737G+ spot welder) and hoping to further salvage the individual cells on this pack.

Is it possible for me to remove the wrap off of very cell and replace it? My google-fu hasn’t yielded any results looking for heat shrink for each cell. Any leads? Would it be ok to simply wrap each compromised cell with kapton tape instead?

Lesson learned. Never purchasing mass produced pre-built battery packs for any DIY build ever again and building my own from here on out. This has actually inspired me to seriously consider starting a battery build service because I actually have empathy and standards that I like to exceed. I don’t want to see anyone get hurt and my goal is to provide packs that take all necessary precautions to reduce the likelihood of injury due to a short.

Thoughts welcome (sorry new users can only put up one pic in a post…)

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what do you mean brittle? they look normal except for the fact that the bms is tugging on them…

Also people have know for a while that mboards sells bad parts, (with some exceptions)

Yes, removing the heat shrink from the cells is fine, and you can easily get replacements, just search for “18650 heat shrink”

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He might mean that the wires are harder than normal, something like crappy quality wire rather than the many-stranded silicon wires that are best to use for this.

as far as i know very few bms’s use silicon wire, all bestech bms’s use hard wire.

Oh you’re right I didn’t look at where the wires went to. I suppose that is the case then, If I were to solder them on though I might have left more space so they weren’t bent like that, but it is Mboards so

What the hell… thank you!

They’re much harder than other BMS’ that I have in my possession and seem to have been exposed to high temps for a long period of time. They seem to be re-used.

dont know how that would be possible…

any reason why you would assume that?

My assumption is based on how hard and brittle they seem to be as some have cracked when bent. They could have also sat around for quite sometime before being used with this BMS. I can only speculate. I’m willing to admit I’m wrong, but they simply do not match the level of quality my Bestech’s wiring possess.

The pack was used once and has sat entirely idle. If it took one exposure to heat for 20 minutes, then the wiring is garbage.

If your not going to reuse those cells hit me up, I’m in the market for some cells to build a few boards.

I’m deciding whether I’m going to build a 2nd DIY or go pre-built, but once I decide I’ll let ya know.

MBoards is based out of Los Vegas area and work out of a ware house there so ya slow baked … …