On Oct 31, 2009, at 11:02 PM, Sean Breheny wrote:

> Hi Gus,
>
> I don't know what "primary NiMH" is. As far as I know, alkaline
> batteries (especially the enhanced capacity ones like the Duracell
> Ultra) have considerably greater capacity than any common rechargeable
> battery. Of course, if you are considering the "total cost of
> ownership" and willing to recharge you batteries many times, and do
> not care too much about the run time per charge, then NiMH would be
> superior to alkaline.
>
> I think that the AA "LiON" batteries you saw were probably not Lithium
> Ion but Lithium Iron Disulfide (see
> http://en.wikipedia.org/wiki/Lithium_battery ). These are 1.5 to 1.6V
> nominal, are not rechargeable, and have much greater capacity than
> alkaline batteries - along with a higher cost.
>
> I would recommend making a spreadsheet using data from the Duracell
> and Energizer web sites, as well as price info from various retailers,
> to compare the cost per energy of alkaline normal, alkaline
> enhanced/ultra, lithium primary, and NiMH types. For the NiMH types,
> amortize the cost of the battery over the cycle life (about 300 cycles
> ideally, perhaps more like 100 cycles in typical consumer use) and add
> in the cost of the charger amortized over perhaps 3 sets of batteries
> worth of cycles.
>
> Sean

You also need to take into account the discharge curve of the battery  
type in question, as well as the consumption of the device you're  
trying to power. Yes, rechargeables have a lower total mAH capacity  
that alkalines, etc, but their voltage/time curve tends to be much  
flatter, especially for NiMH cells. If the thing you're trying to run  
does well in the voltage range that NiMH cells tend to fall in as they  
are discharging, then you can actually get *more* runtime from them  
than alkaline cells.

Unless you have something which needs the full 1.5V from an alkaline  
cell or which MUST be ready to go without needing to muck around with  
keeping charged cells in it (emergency light, etc), you're pretty much  
always going to win with NiCD or NiMH rechargeables.

-Pete
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