Was a while ago, but search eBay for car voltmeter and loads will come up, you can even get an accessory plate with a USB socket one half and voltage display the other (think Amazon do that too).
Find a small one that will suit the bike and where you want it, and wire it into a switched live somewhere (mine is off the side light).
Depending on where you take the live from the voltage could be out slightly to the actual battery terminals, but it will be near enough to show when you have an issue
Find a small one that will suit the bike and where you want it, and wire it into a switched live somewhere (mine is off the side light).
Depending on where you take the live from the voltage could be out slightly to the actual battery terminals, but it will be near enough to show when you have an issue