West Mountain Radio's Computerized Battery Analyzer ($100) is the tool I use to determine which of the zillions of battery packs I own are still performing as they should and which go to recycling.

The CBA is a USB device that plugs into the battery you want to test on one side and your computer on the other.

It comes with software that allows you to set testing parameters and record the results. You can also print a graph of your battery's performance, even across multiple tests. (Click on the screen image for a larger version).

I use my CBA to periodically test my UPS batteries as well as the ones I'd use for emergency communications. It can also test laptop batteries. Be aware, however, that you will probably need to fabricate a cable to connect the battery to the CBA.

This is not an automobile load tester, however, and is designed to draw down a battery at a consistent voltage over time. Click the link above to read the technical specs.

This is not a device I use every day or even every week, and some will consider it a tad expensive for only occasional use. If that's the case for you, perhaps you can find other similarly-crazed battery geeks to combine funds and share one.

Having a CBA (and using it) means never having a battery die unexpectedly.