Marathon Plus 26 x 2.0 Tour:
https://www.ebay.co.uk/p/Clearance-Pair-Schwalbe-Marathon-Plus-Tour-700-X-40c-Bike-Cycle-Tyres-42-622/2297490012
Rain water will run straight through the controller compartment, through a large gap where the cables come out near the bottom bracket, just below the battery.
The only danger is rain water getting into the thumb throttle and the LCD. Keep the LCD glass tilted so rain water won't dwell on its surface.
First, get to know the voltage indicator on the LCD. It has 5 segments, each represents 20% remaining charge, so 5 bars mean 80%+ remaining, 4 bars 60%+ remaining, 3 bars 40% plus remaining, 2 bars 20% plus, 1 bar: less than 20% in the tank.
When you draw a lot of current from the battery, like climbing a hill on throttle, the voltage drops another bar or two, when you ride normally on assist mode, the voltage indicator comes back to normal. To be sure of the reading how much left in the tank, stop for a minute before reading.
There is a technique to get the most miles out of a full charge.
Use the lowest pedal assist setting you can, override the assist level when necessary with the throttle.
Typically, leave the assist level on 1 or 2 or 3.
When you are down to 3 bars, use assist level 3 or less, when you are down to 2 bars, use level 2 or less and don't worry when you see 2 bars! There is still enough for 20-30 miles on assist.
Typically, people get about 55 miles out of a 17AH battery.
Power consumption is proportional to speed cubed. Don't derestrict the bike if you want more miles.