Taking prebuilt pack out of casing to fit in smaller space?

I’m new to ebikes and brand new to this forum, so please direct me if this is in the wrong area or has been answered many times elsewhere. I’ve been doing my reading, but sometimes searches don’t turn up answers even when they exist...

Anyway, I’m building my first ebike from a full suspension MTB frame and therefore have a small main triangle to work with. I’m also trying to do this on a budget and don’t own the tools to build my own pack. My thought was to perhaps buy a battery pack and take it out of the bulky plastic casing and hopefully have a much smaller pack to work with. I’ve never opened up one of these casings, though. How much bulk would one hope to reduce? I assume the BMS is within the casing and might need to be soldered to the pack? Or would it already be attached directly to the batteries? Would something like this be safe to run in the rain if it were wrapped well with plastic? I have basically 33x6cm or 29x8cm to work with. Basically, being a triangle, the longer the pack, the shorter it has to be to fit the narrowing end of the triangle. Right now I’m looking at a pack from PSWpower. $160 shipped for a 13Ah battery pack and charger seems pretty unbeatable if it would fit the bike. They do have a pack with Samsung cells and a little more capacity, but it’s a bigger casing. I don’t know how much of that is just casing vs the battery pack actually being bigger. Any overall thoughts or advice?
http://www.pswpower.com/ven.php?cargo.2018-9p-r5xk
http://www.pswpower.com/ven.php?cargo.2018-2v-jesm

so if its 10s5p of 18650's a good estimate would be
L 18 x 10 = 180mm
H 18 x 5 =90mm
W =65mm

the bms is already attached to the battery and the whole thing is shrink wrapped

It's not a good idea to take a battery pack out of its protective casing. You'll need to give it some kind of protection against dents and moisture, and it's not likely you'll be able to do it in a much smaller space than the battery pack manufacturer (though you might change it to a better shape for your setup).

If that's your inclination, I suggest building your own pack from loose cells. There are lots of threads here with information and resources for doing that.

Not a good idea. Well designed cases don't waste much space or weight. You probably need a battery designed for your space - maybe a triangle one.

There are places that can build you a custom pack; but since they will likely build from good cells, they also likely wont' be as cheap as the generic crap that comes in some of the cheapest premade batteries.

EM3EV makes triangle packs, and may make custom ones. There's smoe members that are packmakers in the for sale section, too, I think.


If you really want to build your own case for one, I recommend going thru the Homemade Battery Casing thread. But to actually build it, you'd have to have the battery it'd be build around in your hands, to be sure of it's actual measurements and shape.

As for size, the site quotes ~43x11x9cm for the casing. If Devo is correct that the pack itself would come to ~18x9x6.5cm, that is a pretty substantial size difference. The length is the big problem I’m running into. And I don’t think it’s just that it’s a crappy product. It’s Samsung cells in a nice looking case with a USB plug to charge accessories. It just seems like all standard casings are too long for a full suspension frame. I can’t spend $600 on a custom triangle pack, or $200 on a welder and then the other supplies needed to build a pack. ...Which I’d then have to do the same thing housing-wise as if I bought a pack and took it out of the casing, right? I guess I don’t understand the difference between building a pack, wiring it up, and housing it vs. taking a prebuilt pack out of the casing?

It will be fine, as long as you really water seal it, with drip loops in the wires and whatnot. Its harder that it would seem to seal up the wire exits. I have several that were the wrong shape, that I took out of the cases, split in two, reconfigured and wired them back together. Starting with a pack that has plastic cell spacers is a plus, and using can cells... I wouldn't do it with pouch cell as they're too easy to damage or get puffed without containment. Some packs start with more wasted space than others, so hard to know how much space you'll gain. If you're going actual trail riding, you might consider going backpack battery....




This was a set of 4 packs the wrong shape... the bottom one is still in the case for support, that the one on top of it was too big to fit, so its been pushed out of its case but still in the FRP covers, then the top two got opened up, then split to be long and skinny then sealed up.

Electric Earth said:

My thought was to perhaps buy a battery pack and take it out of the bulky plastic casing and hopefully have a much smaller pack to work with.

Click to expand...

I'd consider modification of the case rather than replacing it. A 3D printed replacement for part of the case - or even fiberglass/resin - might work for you.

most of the wasted space are on either end. If you just take off the end caps and keep the middle metal case you'll save a lot of space. I have 4 similar packs and that's what I did on all of them. I'm not really following what the others are suggesting, making your own pack is much more labor intensive. Just go for it, its a cheap pack. Like I said, its most likely shrink wrapped already with a layer of polycarbonate underneath so plenty protected already without the metal case

Can we see a pic of the bike or what bike are you working with ?

I don’t have a picture, but it’s a Schwinn S-15 frame. Absolutely nothing on it is original. It now has a Fox fork, a real rear shock, Shimano SLX crank, Avid hydraulic front and rear brakes, Thompson stem, Answer bars, Selle Italia seat, and currently a nice wheel-set and shifter/derailers, though those will have to change when I swap it over to electric. I do already have a WTB front wheel for it that matches the rear hub drive wheel pretty well. I need to find some 7sp Shimano trigger shifters and rear derailer to match the freewheel on the hub motor. I’m gonna just leave the XT front derailer on it. It should be a pretty decent bike. I built it up briefly in the past with the electric kit, but with SLA batteries strapped to the frame. Of course that wasn’t ideal. It rode well enough, though. It should be much better with a lipo battery pack. I’m planning on putting a rack on the front and using the bike for food delivery. The main concern I have is making it safe to ride in the rain. I’m running Schwalbe Big Ben tires in 26x2.5”. I think it should be a really decent bike, and a really smooth ride over anything I could possibly encounter on the road, or even cruising off of sidewalk curbs, etc.