I bought 12v trigger board from AliExpress for different thing (medical device) since its own battery was 150€ and using usb-c pd brick was 1/5 of the price.
Works really well, no complaints from here. It takes 2A of current only so that might be limiting factor.
You should never do that, there are still exposed parts that will not like water (especially pool water) like charging port. If warranty does not cover any water damage you should not treat the device as water proof, only resistant.