I have a 19 Rover (3500 miles), 20 Rover step-thru (3000 miles) that I am a fair weather street and bike path rider.   Besides brakes the 19 nylon gearset failed at 2300 miles the 20 has been trouble-free.
I was thinking of selling both and buying a new non Rad bike, instead I installed Zoom hydraulic brakes on both.  I have put about 100 miles on both and very happy.
IMO I would look to buy a battery or a used 19/20 Rover and use that battery when you use your 18 as commuter.

I had been toying around upgrading to hydraulic brakes on my two RadRover's.   Both bikes have about 3 thousand miles on them and the mechanical brakes have worked fine.  Doing some research there is a ton of options so I decided to wait until this winter.  Plans changed when my 2019 Rover's rear brake cable snapped, I was going to just replace the cable but it was not budging.  I ended up going with CooMeng  Zoom HB876E. 
https://amzn.to/3K0N1uu
I found the install pretty easy considering the vague instructions.
I have ridden about 50 miles and very happy so far.

Looking for recommendations on what to buy for hydraulic brake upgrade for my RadRover5?  Rotors too?  Thanks Terry