With the capacity increase of the AA format batteries, going up to 2700 mAh, came also the problem of high self-discharge. At the point where it was necessary to charge the battery just before to go to fly.
2 years ago, I heard about this new technology called Eneloop and developed by Sanyo. I gave a try and I now use Eneloop batteries for 2 years and I’m fully satisfied. No more need for last-minute charging or frequent re-charging to have a full battery at hand when needed.
I use Eneloop not only in my sailplanes but also in my digital camera.
The only drawback is that Eneloop exists exist only in two formats: AA (Type R6) which is suitable for receiver batteries 4 or 5 cells, and AAA format, which is ideal for small gliders like the Weasel for exemple.
More information in the Eneloop user manual.
Apart Eneloop, I obtained also satisfactory results with Enrich Power (http://www.enrichpower.com.cn/) and Intellect batteries.