Does putting an ipad on a metal surface drain the battery?

I found attaching my iPad to the side of a lockable metal storage cabinet in my office using its magnets is a convenient way to store it inside the cabinet, since it's in a position where it's safe from harm and easy to take out when I need it. It's in a case with an integral keyboard, so scratching it is not an issue.

But I've often been unpleasantly surprised to find the battery is drained, sometimes completely (i.e. won't start up until I connect it to the charger), the next time I grab it to use it on a trip. I have only used it about a dozen times since I bought it new in 2024, so it can't the battery degrading over time due to constant use and recharging. It doesn't make sense to me that I could charge it up, shut it down, put it away, and then find the battery is drained the next time I start it up a few weeks later.

Could attaching it to a metal surface be the problem? Or does an iPad battery leak enough power over a few weeks to explain this?