I just did the 51R upgrade today - the original 2020 battery wouldn't start the car. It went as planned - even the battery protector sleeve fit the 51R perfectly. I took a pic to compare the two styles of battery tray:


Plenty of debris in the old tray. After finishing the car, I took the tray inside and sprinkled some baking soda on the wet looking residue - it fizzed. Up until the last oil change, this car had gotten nothing but Honda service. While I can't rule out one of them topping up the cells and causing an overflow, you should assume any lead-acid car battery will leak at some point. Even AGM and SLA batteries deserve some caution (mount upright where possible, a tray or even a plastic sheeting "battery diaper" wouldn't hurt).