After all our new landscaping I have now reduced the walk behind mower time from 35 minutes to around 10 minutes.  So, I decided to sell my venerable old 2003 lawn boy 2 stroker and send it to a home where it will be happier.  I will miss the old girl, but time to move on. 
So as the title indicates I have decided to take a chance and get a cordless electric lawnmower that is much lighter than the old LB and easier for this old fart to handle and not have to pull a rope starter anymore.  The old shoulder Bursitis did not like the recoil starter.  Pushing a button to start like my pickup is right up my alley these days.  LOL.
So, to my question, can I hose out the underside of the mower deck like I used to do after every mowing with a garden hose.  I can see what I believe to be an electric motor attached to a shaft that powers the rear wheels.  I do not want to assume the motor is sealed and waterproof which it must be to withstand a direct spray with a hose. 
As an experiment trying out the new mower I was able to mow for 45 minutes, 13,000 square feet all using self propel on fairly level ground.  6 AH battery. 
I read somewhere Ryobi 40V batteries are LifePo4, however I have been unable to confirm. Does anyone know for sure?  They are certainly heavy enough to be LifePo4. 
Thank you and sorry for the long post.  Cheers.