Diaries of a Nokia Fan Boy

During my readings today I stumbled across Engadget’s review of PowerGenix NiZn batteries. From a glimpse at the numbers in the review it looked like the batteries the batteries were a much needed improvement in the space of mobile gadgetry:

• 1.6V nominal Voltage
• 30%-50% longer usage on a single charge
• Better able to produce high current

While the review doesn’t specify, I’m guessing that Engadget was comparing the PowerGenix NiZn AA cells (known) to Energizer’s ‘Ultimate Lithium’ AA cells (unknown), in a Speedlight SB-600 hot-shoe flash (known). Anyone having used hot-shoe flashes knows just how demanding they are of batteries, and how quickly they can chew through them, so the test is good.

What surprised me is that they did not post the mAh rating of those batteries. Indeed, even after poking around PowerGenix’ website I could only find a mWh rating of 2500 mWh for a AA cell. Of course, wanting to compare to some of the high capacity NiMH batteries that rating was useless so I found a conversion:

mWhrs = mAhrs * Votlage * hrs (originating from P = I * V)
moving some of the variables around we get:
mAhrs = mWhrs / Voltage (since hrs = 1)
so:
mAhrs = 2500 mWhrs / 1.6V
mAhrs = 1560 mAhrs

That means that these batteries have almost half the capacity of NiMH (high cap NiMH ~3000 mAhrs). Now at first I found this quite confusing since 1500 mAhrs would not be enough to charge the flash 300-400 times. And then I realised that I’m in fact basing my comparison on a worst-case scenario for the batteries. First of all, NiMH batteries are afraid of fast discharge scenarios, and a hot-shoe flash is definitely a fast discharge, second of all, the hot shoe flash works much better with the higher voltage batteries (NiZn 1.6V vs. NiMH 1.2V). In fact, that assumption is built into the review as well, and I believe a different review would be required for longevity in low-current, low-power devices, perhaps a wireless mouse or keyboard.

So my conclusion is actually similar to Engadget’s: if you’re using the batteries in a high-power, high-current device such as a hot-shoe flash, then these batteries are for you. The otherwise, however, is unknown. While I would expect the NiZn to lose out in a low-demand scenario, such as a wireless keyboard, I just don’t know how well those batteries keep their charge. Case in point: my keyboard lasts months on four AA Eneloop cells, and at those time frames its the self-discharge rate that comes into play, not necessarily the capacity.

I guess every battery has its purpose, and this is a rechargeable battery that has long been missing from the options list.

-Nokia FanBoy

read:
PowerGenix
Engadget Review