stromer power plug cap

Hi, I need some help with my bike. I recently got a hand me down ST1, but it is not responsive. Battery (gold variety) reads ~5v on my hand-held volt meter. Most likely this is why the computer won't start. I have a Stromer charger (the one without an "on/off" switch, and one light that...

Do Stromer bikes usually come with a power port plug cap? In a manual picture, it shows removing the cap, but all the "live" pictures of the Stromers I've seen don't show one. I just bought rain covers and plan to ride all weather. At a minimum, I'll put some electrical tape over the plug...