Great Post!NIMH is old technology, especially the older generation NIMH cells: they have the highest natural discharge rate of any rechargeable battery on the market. Newer NIMH batteries with the marketed "low natural discharge" retain 85% charge after one year of non use. However, they don't have as high of a capacity as the older NIMH batteries.
A123 batteries, li-po or li-ion would be the way to go as far as current technology, A123 preferred. They have higher charge/discharge capabilities and are MUCH more stable.