Does anyone use the D size battery anymore? I was going through my battery storage container inventory the other day to see if I needed to buy any new batteries. I have a handful of D size battery rechargeables, and it got me to thinking about it… First, the energy storage capacity of a D size battery is enormous compared with the most common consumer battery (AA size). Sure, the D size is bigger, but it sure packs a punch. D size battery capacity is typically 12,000 mAh (Alkaline) AA size battery capacity is typically 2,700 mAh (Alkaline) More: New Improved Eneloop Rechargeable Battery AA & AAA More: Batteries That Will Not Leak Or Corrode Why do they make a D size battery? Answer: For devices that require a lot of power. Do you know what was one of the most common uses for the D size battery? (“was”) Answer: Flashlights! (and ‘boom boxes’) Times have changed though regarding flashlights. Back in the “old days” there was no such thing as LED flashlights. Flashlights back then mostly had incandescent light bulbs, and they sucked up a lot of power. You needed D size batteries to keep that flashlight going – especially if it had a bright bulb. Today however the LED bulbs require MUCH LESS POWER (drastically less) to achieve equivalent light (lumens) output as the old incandescent bulbs. So the requirement for big D batteries is nearly gone for flashlights… BUT! Hold your horses… I thought of an interesting advantage: Knowing that LED flashlights require much less power than old style flashlights, imagine how long a LED flashlight might operate with larger D size batteries?? How many of you have one of those full size Maglights from yesteryear? I have a few, and they all take the D size battery (one of them takes 6 of that size!). Did you know that you can get LED replacement bulbs for those Maglight Flashlights?? Do you know how long a converted Maglight will function with all those D batteries? Even with the brightest LED replacement bulb (which draws more power) the batteries will last about twice as long. I found what is apparently the brightest available replacement LED bulb for 3 – 6 D or C cell Maglight flashlights (300 Lumen). They’re made in the UK: Maglite LED Conversion Upgrade Cree 300 Lumen Bulb After thinking about it, I have just two types of electronic devices that take the D size battery. My old Maglights and several battery powered LED motion lights that I use inside my shed.