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(Len S) writes:
One by one, people will realize that NiMH never really lives up to
expectations. I have gone through a small fortune in cell phones,
digital cameras, and other doodads (OK, I'm a gadget hound) over the
last five years. Many developed useless NiMH batteries in only a few
months.

How did you charge them? Did you use a good fast charger?

I've had a number of NiMH cells fail, but they were 5 years old or
more.

1) NiMH does have memory effect (they may not call it that, but what
else can you call it when you are told to deep cycle a battery to
"fix" it?

There are several use-related and charging-related effects that may
affect the apparent capacity of a NiMH cell. You don't need to learn
about them if you don't want, but that doesn't justify calling it
"memory effect" when it's something else.

From what I've read (the Cadex book), NiMH cells should be given a full
discharge once a month or once every couple of months to keep the nickel
electrode in good shape. If you recharge every day, that's a tiny
fraction of the charge cycles.

2) NiMH self discharge is far worse than Li-Ion. I hate picking up
something that has been charged withing a few weeks and finding it
dead. If you have NiMH cells, get used to this.

NiMH self-discharge *is* higher than LiIon. However, it takes many months
for them to be dead. In a few weeks, you might see 20 or 30% reduction
in capacity. If your cells are dead in "a few weeks", either you have
bad cells, or they're in a device that puts a constant load on them.
For example, many electronic devices with electronic "power" switches
actually draw current when "off".

When I know I'm going to use a device with NiMH batteries, and I haven't
used it for a while, I'll just pop the batteries into a fast charger.
They're back to *full* charge in 15 minutes, ready to use. It's pretty
seldom that I don't have 15 minutes advance warning of needing a
battery-powered device.

3) Yes, Li-Ion cells are proprietary, but who cares if you can plug in
a camera and then use it for a few days.

Some people care what a spare battery costs. Some people like having a
"pool" of NiMH cells that they can use in any device. Some people like
having a choice of chargers.

5) Notice that no decent notebook computer or cell phone uses NiMH any
more. These products now have brutal price pressure so the makers
would love to use cheaper batteries. They did use NiMH for a while,
but had to stop because the performance was just too crappy.

I think this had more to do with weight. A LiIon battery storing a
certain amount of energy is about half the weight of an equivalent
NiMH battery. The battery is a significant chunk of the weight of
either a cellphone or laptop.

It just so happens that I have a laptop computer with a LiIon battery.
The battery is nearly dead, and provides only 5-10 minutes of running
time. The battery cannot be taken apart and rebuilt with new cells; I
have to buy a new one. (New ones cost CDN$200-300!) This doesn't mean
that all LiIon batteries are bad, but it does provide a counterexample
to the "LiIon batteries are always wonderful" message.

Dave