I just helped a fellow pilot test his batteries because he was having in-flight issues with a low battery after just 2 hours. It turned out that his brand new 12Vdc 14Ah battery was defective.

We tested using a 1.2A load (http://aviation.derosaweb.net/#batterytest). His other batteries lasted 5-6 hours at that high load level. We measured his real load by adding one device at a time to the grid. The "all on" load at 1A (constant transmit, audio vario beeping, etc). The somewhat surprising big power hog turned out to be the charging of the battery in his PDA.