Originally Posted by
mmeiser
It's important to note that some of the higher end and higher mAh batteries will really push the envelop of voltage. For example I've found Energizer Ultimate Lithium AA's typically run about 1.9 volts.
Really, that high? I'm skeptical. Some googling shows no evidence of this, and really, if this were the case, people would be blaming them for all sorts of failures of electronic devices -- and some of it would even be justified.
(Though I don't buy these "lithium" AA batteries -- too expensive, not rechargeable -- so I guess I'll never know.)
Indeed most AA batteries measure way over the 1.2 volts they're typically suppose to put out. What's more if you've read up on NiZn AA's (the latest greatest rechargeable technology for high demand devices like digital cameras) you'll note that people regularly report that these push the voltage envelope for a typical AA. Some have even reported damage to their devices.
NiZn AA's are still pretty rare. And yes, if they have a nominal rating of 1.6 volts and a discharge curve similar to NiCd/NiMH -- then they probably start at 1.88 volts or so. Most items are likely to be OK with this, but it certainly could damage some items, and I'll bet those packages have warnings to that effect. Are you sure you're not thinking of NiZn batteries when you think of the 1.9 volts?
NiMH and NiCd batteries have a "nominal" rating of 1.2 volts -- but they start at about 1.41 volts fully charged. This is well known. Alkaline batteries have a "nominal" rating of 1.5 volts -- but that's when fully charged, it's all down hill from there. So their voltages are pretty close to each other, closer than people give them credit for.
One thing that's worth mentioning (and possibly useful to the original poster) is that the only way you can make a battery of a given size and chemistry have more capacity nowadays is to replace other bits with more electrolyte -- smaller electrodes, thinner case, etc. So a 2500 mAh cell is likely to have a higher internal resistance than a 2000 mAh -- so the 2000 mAh cell may actually make your light a bit
brighter than the 2500 maH cell. The difference is likely tiny with lights, but it can matter with other things. Ultimately, the way you get over 2000 mAh for AA NiMH cells is to skimp on other stuff -- so the higher capacity cells are not always better.
Personally, I'm
really fond of the low self discharge rate NiMH cells nowadays -- Eneloops, Rayovac 4.0, etc. Well worth the extra money (and really, lately it's not even much extra money.)
The key is that everything is standardizing around USB for charging and syncing. This is a great thing since one can theoretically make a secondary battery pack that will power multiple devices. The key element to these simple battery packs is a resistor. For example Radioshack sells a 5-volt resistor for $1.47.
As somebody else pointed out, you have described is a linear regulator, not a resistor. And as they also pointed out, they're inefficient -- a switching DC-DC power supply is more efficient, though depending on the application it may not matter. (Heat is often a big problem with linear regulators, as all that excess voltage is turned into heat.)