After many years in this hobby and not really worrying too much about such a mundane topic as batteries (just buy new ones) I had my eyes opened when I suddenly and violently lost a rather valuable model in a full on power dive from about 200 feet. I had checked the battery just before take off and it read "good". NOT!
The voltage was up, but the capacity was down, way down.

To make a long story short I looked into the PEAK electronics "SIRIUS" line of chargers and testers. They claimed that their system would erase the "memory " of a ni-cad and in many cases rejuvinate an appearantly dead one. I bought the PRO series charger and the Super Test battery tester. I hooked up a 10 year old 500ma 9v transmitter battery that I knew was funky. The tester showed that it had a capacity of only 200 ma, but the instructions said to charge it and discharge it on the Super Test and few times and it would probably rejuvinate. Did it 4 times and only got around 200ma on all the tries. Was about to give up, but thought I would try one more time. Suddenly it jumped to 450 ma and on the last try it went to 575 ma. I be a believer!! I'm cycling all my batteries now and I am really amazed at how bad some stuff was and how good it is now. Best $200 I ever spent when you consider the cost of batteries not to mention wrecked planes.

Bish
K7QCP