Mobile battery test
So, I've ended up with four batteries for my Gnex, but I only have one back-up charger. The most sensible thing it seems would be to take my two best batteries, and keep one in the device and one in the charger at any given time, but it's hard to know which batteries are better, I don't even know which two are the newest at this point.
What's the best way to tell which of my batteries is objectively the best of the group? I know there are lots of apps for this, I can see them in the store, but do they actually do anything? Has anyone used one that they recommend?