SMART Battery box

there are lots of these available. seem too good to be true

Some have 12V, 9V, 5V + USB. Some include inverters. drop your 12v battery in & get going.

Smart Battery box

looks pretty good to use surplus batteries as usb chargers etc. some even support lifepo4

for indoor use, do they need to be grounded? what about if they have an inverter inside? will a faulty appliance cause ground reference to be the user via usb or 12v?

this one looks better:

https://hardkorr.com/us/product/heavy-duty-battery-box/

guess it looks like whoever bought one of these isnt around to tell the tale ?