I have a DC and a AC meter. I picked up ones with blue digital readouts on Ebay for around $5 including the shipping 2 yrs ago. I mounted them in a kitchen cabinet panel just inside the entry door. There at eye level from outside the 5er and the blue light makes a nice night light for the steps into the bath/bedroom.
I wired in a on/off rocker switch. I leave them on most of the time. The 5er's been plugged in here at home for 2 months and they've been on the whole time.
2012 Chevy 3500HD Dually 4X4
Crew Cab long bed 6.0 gasser 4.10
2019 Open Range OF337RLS
Yamaha EF3000iSE
retired gadgetman