Link: http://bit.ly/kbikevoltmeter

I bought this one on eBay last year - not hardwired, probably not waterproof and only comes in red LED - but has served me well* and is accurate. It plugs into the BMW/Powerlet/Hella port and is useful for charging a mobile phone, Bluetooth headset or GPS whilst on the road.
I think I paid the equivalent of two grape leaves and a figbar for it, coming from China as everything seems to lately, but the latest starring actress.




*the plastic snap-on/off cover came off after about 3.8 seconds, faster than my red K100RS to 60 mph.