I started having a starting issue with my BMW last week. The symptoms were similar to that of a weak battery. On my R100 I had a voltmeter built into the fairing but, on my R1100S and on my Ducati, I do not have one.
I do however have the quick connects on both bikes attached to the batteries on both bikes. While it is quite easy to use a multimeter to check the voltage both running and with the engine off, it is also awkward to do and may times not convenient.
I found the voltage indicator from Battery Tender on Amazon for 15 bucks and thought I would give it a shot. Well, I could not be happier. It plugs right in to the quick connect and tells me the voltage with or without the engine running. Pretty simple. With the engine off, it should read 12.5v and with the enginge running, it should read 14.4v.
There are only 2 drawbacks. The first is that it would be nice if it were backlit. The second is that I would like it if there were some type of clip or way to attach it to the motorcycle.