It had never occurred to me until I saw a comment on another thread that an ebike battery would not be waterproof. Not sure if the link/image below will come out, but its a downtube battery with a round connector on to the removable battery. I can supply actual photos if it would help. The wires into the bottom on the bracket have a braided sleeve, but the hole is probably 10mm and its facing any spray coming from the road/front wheel. Plenty of space for water to get in. Can it do any harm in there ? Should I fill it with silicon ?

 

https://www.amazon.co.uk/gp/product/B071GN86HS/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

Those ones aren't too bad. I've been out in some very heavy rain without any problems, but, as a general rule, you shouldn't leave your bike out in the rain.

You should be OK, but as Dave says, you shouldn’t store the bike outside in the elements.

 

Advice for anyone carrying an ebike on a car or motor home rack: Always remove the battery before transporting an ebike. The ultra fine spray created in the vortex behind your vehicle in rainy conditions, will hit your battery at jet wash speeds, and is likely to get in to the battery case.

I had reason to split the case on my Das Kit/Oxygen battery and was amazed to find that there was little or no water ingress protection. I put it back together and silicon sealed the joints as best I could, but I doubt it is anywhere near waterproof even now. Even more worrying is that the controller is part of the battery case/mounting and that looked as vulnerable as the battery.

 

On my converted bike, I've placed the controller into a saddlepack that offers a good deal more protection.