ORIGINAL: Rodney
Yes, they do self discharge but at a very low rate. Since man has not yet invented a perfect insulator, all batteries will self discharge with the rate determined by the quality of the insulation between the plates and contamination between the two poles.
Answers something I've pondered over. I find a day after balance charging to 4.2 per cell a day later they will measure in the range of 4.16 to 4.18 per cell. They appear to level off at that range at least for a few days. Topping them off only puts 30 - 40mah back in a 3 cell 2200mah pack in my case, so hardly worth it IMO.