My new 9 watt LED light (intended for use in RVs) says it can handle 12-20v:

http://www.amazon.com/dp/B0098YKVSU

I want to use this as a high-brightness LED light in a shed, so I don't have to deal with wattage losses from using 120v AC LED lamps and then also needing an inverter to make the lamp work.


I don't know yet if I want to fiddle with a 12v lead-acid gel cell and a solar panel. I want to try using alkaline primary cells first, just to see how long they will last.

I'm also going to use a 15 minute mechanical bathroom timer to limit the On-time for the lamp and to try to prolong the battery life.


I'd prefer to use more alkaline cells for a higher voltage and the longest cell rundown time.

If Wikipedia is correct, and 1.65v is the absolute max, then 12 cells = 19.8v .... which is very close to the limit, but apparently still safe.


It'll be used in a small garden shed, and these buildings can get very overheated in the summer.

It'd be rather sad if the cell voltage rose to 1.7 v or more from the heat, and killed the LED lamp one day from someone turning it on.


To try to deal with potential battery heating and voltage rise, I plan to put the battery holders near the floor of the garden shed, on the side that faces away from the sun.

I recognize that a high building temperature will likely lead to more rapid battery failure, even if there is no voltage rise.

 

I don't think higher voltage will affect the brightness - that bulb has an internal current control and brightness is proportional to current. So it's able to take a range of input voltages while supplying the same current to the LEDs and thus the same brightness.

You can test this for yourself to verify.

So maximizing voltage doesn't gain you much. To maximize mAh capacity, you might consider a series-parallel arrangement.

 

If you place the batteries in contact with the floor, that will minimize their temperature rise, since the floor acts as a large heat sink and is likely to be significantly lower in temperature than the adjacent air.