Rehousing 48V 20Ah Battery into Smaller Case?

[Kangrui]

I recently bought a Wallke H6 that accepts a dual-battery setup using a balancer: one 48V 32Ah battery housed under the seat, which came with the bike, and one 48V 20Ah battery housed in the folding frame, which I do not currently have. Wallke offers the second battery directly on their website along with required connectors for ~$720 (Wallke H6 Dual Battery Kit), but I've been trying to directly source the same battery from AliExpress for less.

I found and ordered this battery (https://www.aliexpress.us/item/3256....order_list.order_list_main.11.3e311802LmIW9P), which seemed to match the dimensions of the pictured battery kit (420 x 108 x 68mm), based on my measurements of the frame opening. However, I just received it from China and it doesn't fit into the frame - the actual L x W x H measurements are perfect (checked with someone who has the manufacturer-provided kit and the dimensions are identical), but the chamfered edge of the battery case has a slightly different angle than what the frame accepts (cross-section diagram below, black line is my battery and red line is the frame opening), and I can't slot it in.

The battery itself works great and is brand new, it really just needs a couple mm of clearance at the corners in order to fit - if I can't return this battery to seller, is there anything I can safely do to make this battery fit into my frame? Can I sand down the corners of the aluminum case by a few mm or take it to a machine shop to cut the case? Or can I source a slightly smaller case (420 x 105mm) and rehouse the cells? Super frustrated because the battery is so close to fitting and I'd rather not have to return it, and I don't know how easy it is to re-sell a battery like this.

 

[amberwolf]

The battery itself works great and is brand new, it really just needs a couple mm of clearance at the corners in order to fit - if I can't return this battery to seller, is there anything I can safely do to make this battery fit into my frame? Can I sand down the corners of the aluminum case by a few mm or take it to a machine shop to cut the case?

How thick is the case? If it's thinner than the necessary change distance, it can't be sanded down or you'll sand all the way thru it and into whatever is just inside it.

Is the clearance problem actually to clear the frame, or just the entrance to the frame?

Or can I source a slightly smaller case (420 x 105mm) and rehouse the cells? Super frustrated because the battery is so close to fitting and I'd rather not have to return it, and I don't know how easy it is to re-sell a battery like this.

It is not uncommon for the cells to be glued to the casing, so it may be difficult to remove them without cutting the case apart. But if you can remove them, then as long as the pack itself will fit inside whatever other case you buy or make or have made that fits your frame, it would work.

 

[Kangrui]

How thick is the case? If it's thinner than the necessary change distance, it can't be sanded down or you'll sand all the way thru it and into whatever is just inside it.

Is the clearance problem actually to clear the frame, or just the entrance to the frame?

I think it's to clear the frame itself, not just the entrance, which makes this tricky - if it were just the entrance to the frame, I think I could could just sand down the frame opening itself, but the only plausible option I see here is to try to adjust the dimensions of the chamfered edge along the entire 420mm length of the case, which seems much more complicated.

I'm pretty new to this stuff and unfortunately don't have any experience working with metal, so I don't have any sense of how involved of a job this is - is this even doable assuming there's enough case thickness? What tools would I need to work with aluminum?

 

[gromike]

I was going to suggest filing the offendending corners of the battery case until you haven't gone too far, but I like the cutting into the bike's battery cradle. That's going to take some tricky cutting tools, and might make the bike's manufactured batteries less usable. Maybe you should order another one or two of those alliexpress batteries before you do the mod.

 

[docw009]

You want to cut the metal 1-2mm along the whole 420mm length of the battery? The case is probably only 2mm thick at most. Seems to me that the top of the case will be sliced off.

 

[Kangrui]

Yep, you're right - took apart the battery case and there's not enough thickness there to make the adjustment. I decided to just return the battery to the manufacturer at a loss and am now working on a different build!