Flashlights and batteries are interesting subjects. I see we have a couple Lumenaries on the forum, too. I researched the LED lights, the older bulbed lights just are not good technology anymore, not bright and inefficient. I also like Fenix lights and have several, all use AA's. One use is for night hunting and use red and green filters on them. These newer LED lights have adjustable outputs and will go dozens of hours on a low light setting. Good for emergencies or backpacking.
My other lights like the Maglights have been converted over to LEDs. And I have them scattered around, too. I wanted all my lights to take AA's, since they are easy to find and buy...just in case of an emergency. They have to be small, (to fit in my pocket), and bright with a lower kelvin color temperature allowing good color rendition. [SIZE=+1]
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Rechargable batteries...
The best rechargable batteries are Sanyo Eneloops. That's what I have been using. Maybe the other companies have gotten better lately, I don't know. AA batteries in about everything except AAA, (get some of those too).
Rechargeable up to 1800 times.
75% capacity after 5 years of storage. and the newer ones are getting better.
Also...alkalines will leak. These Eneloops are a different chemistry and do not leak and destroy your stuff.
For the Maglights with swollen leaking alkalines in them, you can drill a small hole in the battery bottoms and then screw in a large screw. Then pull the batteries out holding the screw. Take a wire brush, sandpaper, and heavy steel wool to the inside tube. After ruining a few lights and radios, I went to rechargables.
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Below...D spacers...to start...the AA fits in the body of the spacer and it becomes a D cell.
http://www.amazon.com/eneloop-SEC-DSPACER4PK-Spacers-battery-cells/dp/B002V8C3W2/ref=pd_sim_e_5
Look at the chart on the page...select D, C, spacers. Get a number of them. This will allow you to use AA batteries in about everything. Get spares, keep them charged. Chart has batteries, etc.
My two cell D LED Maglights will run almost 2 hours on two AA Eneloops in the D cell spacers.
Then get a charger or two. One of the ones I have is one of these...multi-use for different rechargable batteries... and will take DC from a cigarette lighter adaptor pigtail.
NITECORE
From Amazon...
Amazon.com: Nitecore IntelliCharger i4 Battery Charger - 2nd Generation: Sports & Outdoors
Adaptor...
Amazon.com: MHS-DC12 Car Vehicle Cigarette Lighter Adapter For PowerEx C9000 Nitecore i2 i4: Electronics
I keep spare Eneloops in my truck and cars as well as the house. Just swap them out as needed. Below are the holders I use to keep the batteries together, you can get them in various colors and denominations:
Amazon.com: Storacell: Electronics
Even the mouse I am using with this laptop has an Eneloop in it...
I could go on about solar chargers if you want...