Blind rivet nuts for ebike battery on frame: aluminium or steel?

Question

I'm planning my first installation of an ebike battery by drilling/riveting the frame (photo of the battery below), here are some details about the project:

• The battery weights about 5 kg.
• It's a folding bike, and because of the hinge, the battery won't be close to the frame, but shifted up about 15 mm using spacers between the frame (i.e. the rivets) and the battery support. This adds leverage on sideways force.
• I wish to put at least 4 rivets. Maybe more, by putting 2 close rivets on some holes of the battery support.
• I'm aware steel rivets are much harder to install than aluminium rivets. But I'm planning to buy a good quality clamp, with a lot of leverage.
• I'm considering to use M6 fasteners rather than the standard M5 if there is enough room (in particular for the bolt heads).
• Bolts will most certainly be 12.9 steel.

As you may have guessed, I wish the installation to be really sturdy. The bike will be stressed, and I'm really worried about breaking bolts because of sideways force (for example if the bike falls down). So I want peace of mind about this. Also, I encounter many DIY ebikes having battery wobbling issues, and I'd like to avoid that...

So, steel rivets may seem to be a better pick than aluminium rivets, but I think they have a major drawback: if there is an issue with a rivet (e.g. it gets loose and turns on itself), an aluminium rivet would be very easy to remove, just by drilling it, whereas drilling steel would be much, much more difficult. (I know it, on a screwed up steel bolt, I had to drill for many hours, just to remove a very small amount of material...)

Thus I'm hesitating between aluminium and steel rivets, though I'm bending towards aluminium because of the above issue. What are your insights about this?

Update: Here are some details following up to your first answers and comments:

• The frame is aluminium. By very rough measurement, the wall thickness should be about 2.75~3mm.
• To clarify/emphasize, I'm indeed talking about rivet nuts, aka nivnuts. Not regular rivets.
• I'm aware of galvanic corrosion issues, though in the present case it shouldn't be too hard to manage. (and the bikes are stored indoor, that helps a lot)
• My previous issue with drilling steel could have been because of inadequate drill bits. I can't say, maybe. It was with a Dremel actually (a pretty powerful one, though).

So, shall I opt for steel rivets?

• If ever I had to drill through one, it would be doable by using a good drill bit (like cobalt or carbide), right?
• If ever the rivet started rotating on itself, could I just try first to use the clamp again on it?

Update 2:

• After some more reading, I have established that aluminium rivnuts would be too weak and inadequate for the job. Therefore I'm going to use steel rivnuts.
• People also put some red Loctite (the permanent one), or even JB Weld, when installing; I may go for the Loctite. Using JB Weld sounds overkill, even for me.
• I have created a new question, about the spacing I need to put between the frame and the battery: DIY ebike: what system to choose for adding space between frame and battery?. Your insights are welcome!

Answer 1

Personally? For a heavy battery mounted on raised/cantilevered supports, I'd suggest looking at a welded support and forgo rivets completely.

If you do use rivets, I'd match the metal to the frame to eliminate galvanic corrosion issues. Four rivets might not be enough - depending on how your mounts touch the frame, you might want "foot-like" lugs, with one either side and at least one in the foreward or aft direction.

Or look at mounting rivnuts in the frame instead, and then use decent bolts into those to hold your battery frame.

Batteries are surprisingly heavy - I once made a 3 point bracket for inside a frame's main triangle. It used the bottle cage mounts, along with metal straps to the top and seat tubes. It was barely capable of holding the batteries even with a triangle of stability.