Low Self Discharge NiMH C Cells ( "ready to use" or "pre charged" 4500 mAh) are now being offered on Amazon at US$26 for four. These are branded "Accupower Evolution" and are claimed to have a self discharge rate of 2% per month. This is much lower than the rate for regular NiMH cells of 0.5-1% per day and high capacity cells having the highest self-discharge rates.
I have used smaller AAA and AA low self discharge batteries successfully, but have not yet tried the larger ones. Some tests of the smaller cells by users seem to be inline with the maker's claims.
Accupower are also offering Low self discharge D cells (10,000 mAh) but these do not yet seem to be widely available.
The lower discharge rate batteries might allow the use of smaller batteries in some applications, such as solar home lighting for remote areas using small solar panels. The batteries could be used with efficient LED lights, such as Flexible LED Tape Light emitting diodes (LEDs), to provide light where it is needed. The cost of the batteries and LEDs would be much higher than some alternatives, such as lead acid batteries and fluorescent lights, but because the LEDs can deliver the light where it is needed, the overall cost might be lower.