This is simply not true. Sure lots of bikes - especially the cheap $1000 variety - shouldn't be let sit out. But even for those bikes, you can put baggies and saran wrap and rubber bands over the less-than-IP65 stuff and you are fine. An exposed battery maybe not so much but myself I use enclosed battery bags that I treat with silicone water repellent (or I build into a box where the pack's construction and the box's makeup takes heat into account) and I have bikes with thousands of all-weather miles on them that have no issue whatsoever with water. That includes a 31ah, 52v pack that resides under the cargo floor of a cargo bike, about 4 inches off the pavement.
Nowadays there are displays and throttles that are made to IPX6 standards and they are still actually quite inexpensive. But you have to know what you are looking for of course. Honestly, the baggies work great so I haven't spent a lot of time worrying about it.
Took this pic on the way to work in the middle of a rainstorm in 2020. If the forum doesn't downsize the resolution too much you should be able to see the bike is covered in water, and not from splashing off the ground. Raindrops are visible falling in the pic. No baggies needed thats a garden variety 860C display which is IP65 rated. And your basic Bafang thumb throttle which is also fine in the rain. Plugs are all Higo/Julets which are water resistant, especially when you moisten the connections wit a bit of dielectric grease on assembly.
The 'atmospheric river' we just had here on the coast of California hit me with 10x that level of water for a week.
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