[Elecraft] AA primary cells: NiMH vs. Alkaline

[Wayne Burdick]

Steve,

When we first started demonstrating the K1 with the KBT1, we were using
Alkalines. We'd get maybe one full day out of a fresh pack. Then we
switched to NiMH cells, and we'd get three days!

The problem with Alkalines, as alluded to earlier, is that they have a
sloping discharge curve. They'll drop to the K1's regulation
threshold--about 1.05 volts per cell (8.4 V total for the pack)--long
before they are fully discharged. In fact the mAHr rating on Alkalines
is usually based on discharge to 0.9 volts per cell! Below 1.05
volts/cell they'll be nearly useless for transmitting, because their
internal resistance will have increased significantly. There will be a
large voltage drop when you try to transmit.

NiMH cells, in contrast, will sit between 1.125 and 1.25 volts per cell
for about 90% of their charge life, and even up to the 95% discharge
point they'll be usable on transmit because their internal resistance
stays low. This translates to more operating time.

This alone would favor the NiMH cells, but when you factor in 500-1000
recharge cycles, they're much more cost effective, too. Besides your K1,
you can use them in most consumer products, HTs, etc., so the initial
expense of the cells and charger will quickly be reclaimed. Over a year
ago I bought 16 NiMH cells and the Radio Shack 8 cell AA fast-charger,
and I haven't purchased a single AA cell since.

So in my opinion, there's no comparison: if you're using 8 cells, as
with the KBT1, the NiMH cells win. Alkalines are OK if you're in a hurry
and need some charged cells quickly, or perhaps as a backup pack.

73,
Wayne
N6KR