1 D Cell is equivalent to 4 AA Cells for capacity -

Rechargable NiMh LSD D cells are available such as the Ansmann maxE Rechargable Battery D 8500mAh

http://www.amazon.co.uk/gp/product/B002A...ler=&sr=8-1

They work very well with the Ansmann Powerline 5 chargers

http://www.amazon.co.uk/ANSMANN-POWERlin...8338&sr=8-3

which can be used with a Cigarette Charger output such as provided with a portable PV solar Charge (20-30W panel) or an SLA battery/Solar PV setup.

The D cells once charged work nicely with the Varta 4W LED 3 D cell Lanterns (equivalent to 12 AAs), which have 3 high efficiency Nichia LEDs.

http://www.amazon.co.uk/Varta-4W-LED-Cam...7247433-4786234

These will typically give 300 Lumen for around 6 hrs or 12 hrs on the lower settings. They are quite effective as they can be hanged up side down if used in areas difficult to light.

D cells are also useful for D-cell Maglites with replacement LEDs bulbs. These flashlights are still useful for home use and will typically give out 100 Lumen for around 20 hrs before recharging the NiMh D cells.

The real benefit is having not to constantly recharge so often the smaller AA cells again and again compared to the D cells, which can be a pain.