Improving a Battery Mounting


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Local time
7:58 AM
Dec 17, 2020
Following a 30 km shakedown round trip on my newly converted Trek 800, I've started the process of refining the beastie in the hope of improving reliability, longevity and ease of use and maintenance.

First up, while riding on rough surfaces, I noticed quite a lot of rattling from the battery area.

The battery is a standard 36V, down tube mounted unit, as shown in the attached photo. The mounting plate is bolted on to the downtube bottle cage bosses. My inner engineer doesn't like this for a couple of reasons. The bottle cage bolts are only M5 and are rather close together, meaning that the big, heavy battery is only properly supported at the bottom end, leaving the top end to flap around on bumpy surfaces. The second objection is related, in that the mounting plate is flat, and is bolted down to the round section downtube so, again, there's only limited support preventing that big lump of electricity from swaying from side to side. Altogether, I can see long term use over my regular commuting track resulting in something breaking earlier than it should.

I'll be adding another bolt or two as soon as I can lay hands on a rivnut setter and suitable M5 inserts. In the meantime, I'm concentrating on giving the battery as much support as possible, and adding some rubber mounting. As the proud owner of a laser cutter (which I bought for other interests and never expected to use for bike stuff), it didn't take long to draw up a slot together plywood "kit" for a cradle to fit between downtube and battery mounting plate. There should be a photo nearby of the assembled cradle. There will be a sheet of firm, non-slip rubber between the downtube and the concave side of the cradle, and another between the flat bed of the cradle and the battery mount plate. I've just done a trial fit to the bike and it all goes together nicely, but final fitting will need to wait for me to find some suitable length bolts, as the originals aren't long enough.

While messing about with the battery, I noticed that I could feel the internal cell bank slopping around inside the casing. This also struck me as a recipe for breaking something prematurely, so I decided to have a look inside. Ignoring the label forbidding disassembly of the battery, I pulled out the 8 screws holding the casing together and opened it up. Presumably the manufacturer doesn't want people looking inside because we might find out how crude the internal wiring is, and how many wires were pinched/kinked on the production line. Hey-ho; just more evidence to support my theory that it's often best to regard Chinese products as assembled kits which will need checking and fettling before use. Anyhow, once I'd tidied up the wires a bit, I padded the internals with some of that thin foam wrapping sheet that often comes with printers, laptops and other tech stuff. Screwed it all back together and gave it a good shake. Great. No more clonking and rattling.

I should be able to get it all back together and test ridden in the next day or two. I'll report back as soon as I know if I'm on the right track.
Oops. Forgot to attach the photos.


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Had the opportunity this afternoon to get everything screwed together. A quick test pedal up and down the first kilometer or two of my regular unsealed track showed a great improvement. No worrying rattles or clonks from the scarily expensive battery area. I'm happy with that.

A megacheap rivnut setting tool and some M5 stainless inserts are on the way, so when they arrive I'll be adding a couple of extra bolts to keep it all firmly in place on the downtube.
I wonder if the internal padding is a good idea? You've effectively also insulated the battery pack from any cooling effects the bottle might have had. I guess it depends on the batteries and their use in your situation but I would prefer to let them stay as cool as possible. Just a thought!