installing a battery on a curved downtube


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8:35 AM
Oct 21, 2020
I have a canfield EPO that I have installed a bafang bbso2 mid drive onto.

It was straightforward to install the mid drive except I had to cut off the bash guard mount under the bottom bracket. I just used a hacksaw to get most of it, then a dremel to smooth it down flush.

The problem is the downtube is curved. I cant seem to find any info on how people are installing batteries onto curved downtubes. All pictures seem to be straight downtubes.

I have read some hints of using suguru to fill the gap.

A triangle bag could be an option, but I would prefer to securely mount it to the frame.

Is there a solution that is generally considered to be the best way?
What kind of battery do you have, is it a custom, is it LiPo's (bricks), LiFePO4 (overly heavy and bulky), Lithium Ion (21700's/18650's or Prismatics) , dolphin case, shark case, seat tube case (more cheesy china battery case option, I think they call it frog)
Where did you buy the battery from?

That's why the choice of bicycle to install your ebike kit onto is important. Thankfully your mid drive installed without any problems, some people have had problems because the frame had interferrance with mid drive.

I have seen lots of ways to attach a battery to a frame. Some have used the bottle bosses to fabricate something up, some have used clamps (T-bolt clamps, hose clamps), others built there own enclosure with custom attachment points (built case to and around frame, like fibre glass), triangle bags works well too and is a cheap and easy solution to your problem, lots use them ( "Triangle Bag"). A last ditch option would be grab some black Gorilla Tape duct tape, and metal zip ties which is not appealing to the eye, but it will get you rolling.
I got the kit from bafang direct. I just got one of their batteries in a shark case.

This is my plan:
I have ordered some 1.5 and 2 inch m5 bolts and some moldable plastic. I think the plastic will fill the gap, the bolts will keep the battery from sliding around and zip ties will provide most of the pressure to hold the battery on.

The zip ties almost work by themselves, but the battery slides some while riding on our rocky trails.

The big test is whether the bafang gets beat up by our central texas rocks and ledges.
I've used a Luna triangle bag for five years with no problems. It has two inner straps to hold the battery fairly securely, and I filled the rest of the area with a spare tube and foam. Could be a problem in extremely hot areas with cooling, but not (for me) in socal where it's been as hot as 90+ possibly since I use low PAS levels.
The Luna Bag will be coming from California, the EM3EV bag will come from China. The EM3EV is owned by a British fella who lives in China. Both companies very reputable.
I am glad to see them both still operating and selling ebike parts and kits.

Another even more reputable place to look for mounting gear and anything else ebike related is in Vancouver, BC Canada. They even have custom spokes!

I've done zip ties and duct tape for the battery, hanging off the top tube.

Some people have put their batteries on the bottom side of the downtube (headset to bb tube). Either way you do it, I'd throw on some steel zip ties and heavy duty 180lb plastic zip ties and lots of them. Then hide the zip ties with black gorilla duct tape. Its too easy for thieves to twist regular zip ties off and they'd have your expensive battery.

I dont know how you'd stop the battery from sliding down when mounting it to the downtube, I've always ever attached batteries to the top tube.