Imagine what you could do with one of these:
http://www.parts-express.com/tenergy-industrial-grade-f-cell-rechargeable-nimh-battery-13000mah-with-tabs--142-0237
1.2V when charged, couple this with a boost regulator from pololu and run forever!
Specifications: • End volt of discharge: 1.0 V • Maximum discharge rate (continuous): 40 Amp, Maximum discharge rate (short time) 60 Amp • Charging current: Standard rate: 1280 mA for 16 hours, rapid rate: 2560 mA for 7 hours
Nice.
Does say clearance item, better hurry 8)
What are the dimensions ?
Dimensions: 91.0 mm H x 33.0 mm D • Weight per cell 226 g.
Wouldn't take em for free.
50% longer and almost twice the diameter of an 18650, freaking huge, and a half pound each!
13Ah at 1.1v is 14.3 watt hours.
18650 lithium batteries go up to 3 Ah at 3.7v - 11.1 Wh. Half the price, smaller, lighter, and will run a micro without a boost converter enabling long standby time in sleep, and charging ic/modules are readily available - and 3/4ths as much energy as that monstrosity
Hi,
Yes that is an interesting NiMH battery.
I use mostly the low self discharge type now because they hold a charge much longer when not being used. They are Eneloop or similar. Less capacity but that's the way it goes. I had too many problems with the regular type that lost charge too fast when sitting on the shelf doing nothing. I had Energizers that would self discharge down to half in a week. Got fed up with that.
I also went to Li-ion some time ago also. I get 4.2v at about 2000mAhr to start down to 3.4v near the end of discharge which isnt bad. Some of my lights only take this size anyway though so i have to have them.
I also use 12v Lead Acid, which even at 7Ahr capacity when buck'd down to 3v will exhibit about 28Ahr minus maybe 20 percent. Cost about 20 dollars USD each.
They make bigger ones that would given enormous run times but they are more expensive. I do have one big one though that would run an Uno for about a thousand years 
Ok, realistically maybe 2000 hours, but that's a long time.
Back when we had the (hurricane) four day power outage in my area i had a light running the whole time, off of one of my 12v LA batteries. Didnt even make a dent in the voltage yet