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Battery tech

As a kid, I recall spending inordinate amounts of my pocket money on batteries.

If I had already bought my copy of "TV Century 21" magazine then I'd probably be buying regular batteries. If this worthy sci-fi magazine hadn't come in on the day I collected my cash then I'd opt for the "heavy duty" versions.

From memory, the regular batteries were kind of silver in color, the "heavy duty" ones were black.

The only brand on the market was EverReady and these were the good old zinc-carbon dry cell type. Supposedly, once they went flat they were good for nothing - although cunning young minds had long ago discovered that a few minutes in a warm oven would see them "bounce back for extra life".

Even once the oven-trick stopped working, there were still plenty of uses for such a battery.

The carbon rods were very useful, since they could be used for creating carbon-arc lamps and torches or ground up into a fine powder for making gunpowder. Yes, this was back in the days when kids were allowed to be kids and making your first batch of gunpowder was a rite of passage.

The zinc cases could also be filed into a fine powder which, when mixed with flowers of sulfur, made a brilliant propellant for solid-fueled rockets.

However, as a battery technology, zinc-carbon was very limited and for decades, the crappiness of these batteries really did hold back the development of portable devices.

Rechargeable batteries such as nickel-cadmium and nickel-metal-hydride helped advance the growth of portable electronics by delivering higher energy densities and the ability to be reused.

Both these technologies still had their disadvantages though. Nickel-cadmium cells were prone to voltage depression and dendrite formation - things that drastically reduced the life and capacity of the cell over time. Nickel-metal-hydride cells had a very high rate of self-discharge which meant that they were a poor choice for infrequently used devices.

The self-discharge issues of NiMH cells have been pretty much sorted but I noticed yesterday that nickel-zinc cells are starting to become mainstream - and at very attractive price

I think I'll grab a fist-full of these and see how they perform.

One of the down-sides of NiCd and NiMH cells are that they have a nominal voltage of just 1.2V, a full 0.3V less than the zinc-carbon or alkaline cells they often replace. This can result in reduced performance of some devices and an inability to utilise their full capacity in "smart" appliances that have an auto-shut-off based on voltage.

While lithium-based technology still offers a higher energy density, I would expect the NiZn cells to have a somewhat less spectacular failure mode if physically damaged, overcharged or subjected to a short-circuit load.

Like most folk, I still have a fist-full of devices here that rely on AA cells (TV remotes, wireless mouse, old MP3 player, etc. I'll give these cells a try and see how they work.

The only real drawback I can see for most people is the seeming lack of a suitable charger -- I guess I'll have to knock something up.

Stay tuned -- I'll keep you informed.

Has anyone already tried NiZn cells? If so, what were your experiences and what charger did you use?

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