Chassis for battery pack

After giving it more consideration it seems like the more preferable solution is to have the entire battery pack at one location, so it is easily detached from the frame for charging.

For that I made a "chassis" where all the bricks are gonna sit snugly next to each other,
and mount the whole thing on the top tube, like a fuel tank with motorcycles.
I bought some flat bars, adjusted their lengths with an angle grinder, and used DevCon S31 2 Ton Epoxy with 2500 psi (advertised, should be enough anyways) to glue the pieces. (Note that one piece hasn't been glued yet).

I then dropped the glued bars to the floor, and snap they go! Everything back to pieces. The 2-ton caved like nothing :( it fell from no higher than 70cm.
I think I did everything right - sand-papered the surface then wiped it with acetone before applying and let it cure for 10 hours. In fact, even several days later I was able to peel the residues off with a player, so it's not that strong after all.
 So me and tony 2-ton will go our separate ways, and I'll bolt the bars like I should have from the start.