Does a 1-cell battery in a flashlight tend to have a longer shelf life than 2-cells in a comparable flashlight? Whenever I pick up my 2-cell flashlights after months of non-use, they're always dead. Meanwhile, my 1-cell flashlights work fine.

Is it just my luck or is there a theoretical explanation? For example, does the 1-cell flashlight naturally short a circuit to contain energy efficiently within the single battery, while such containment is not as pure for 2-cells touching each other? Of course, I'm talking about keeping the 2-cells in there as normal, not reversing a cell or doing some other trick.

Nowadays, I buy 1-cell flashlights exclusively since the advent of LED. Personally, I've never in my lifetime needed more emergency light than what the modern 1AA LED flashlights provide. I don't dispute that some folks need more light. Another advantage is a 1-cell flashlight is as simple as you can get, battery-wise. For me, simple is better, unless there is a compelling reason to go more complex. Also, I find myself bringing a 1-cell flashlight with me, while the bigger flashlights are stored away somewhere, no matter how cool the bigger flashlight is.

No. Parasitic drain has basically nothing to do with how many cells are in a flashlight, and everything to do with how the circuit and switching is accomplished. Some flashlights can be "locked out" to be completely off if stored for long periods between uses. Alternatively you could remove the batteries if they're not to be used for a while.

I separate the batteries and lights if the light is going to be stored for any length of time. Lights in my GHB and other kits are packed separate from their batteries, except for my survival vest and flight bag. These are all primary lithium batteries with lots of shelf life remaining.

i find that multi-celled lights aren't as reliable as single cell because they have more contacts to corrode, and if one cell fails, there other(s) can't do the job.

thus, when i can, i prefer single-cell models with extra batteries carried separately.

also, i don't leave alkalines in any flashlight. instead i store them with lithiums or NiMH rechargeables.

and if you've been buying multi-celled lights because they're brighter, maybe a brighter higher-end single-cell is your answer.

ie: a carefully chosen 1xAA light can pump out much more light than most versions offered in hardware or sporting-goods stores.

I mostly use ordinary alkaline batteries, usually from Costco, and haven't had a lot of problems. Off hand I can only think of one time I've had a light wrecked by leaking batteries, that was a mini-mag that got lost and then I found it again several years later. Maybe I'm just lucky? Of course it does tend to get dark up here in Alaska in the winter, so maybe it is just because I just use my lights often enough, and thus replace the batteries regularly.

I have various vintages of Princeton Tec, Pelican, and Mini-mag lights. I've had good luck with all of these brands. The newer ones are LED, but the older ones are not.

I also have an extra couple of cheap, older style flashlights I keep stashed in our cars. One trick I use with these is to reverse one of the two batteries while they are stored. Cheaper lights often have a not so secure on-off switch, and by reversing a cell they don't discharge even if the switch gets bumped. Of course it takes a moment to open the light and switch the batteries back. Alternatively, I have sometimes put a small tab of tape over the switch to make sure it stays off.