Re: Do NiMH batteries leak?
- From: ASAAR <caught@xxxxxx>
- Date: Mon, 29 Dec 2008 13:33:19 -0500
On Mon, 29 Dec 2008 04:42:21 -0800 (PST),
wannabesomeonecares@xxxxxxxxx wrote:
It's likely that they would, eventually, but it would probably
take a lot longer to leak than is typical for alkalines. A year or
two ago I stumbled upon a battery pack that contained 8 AA 450mAh
Radio Shack NiCd cells (for an old CB walkie-talkie) and there was
gross leakage from almost all of the cells (I don't recall if it was
6 or 7) that was much worse than the leakage than I've ever seen
from alkalines. They were stored in a bookcase for about 10 years,
give or take a couple, and they weren't subject to temperature or
humidity extremes. The chemistry of NiCd and NiMH cells is similar
according to manufacturer's application manuals so I wouldn't want
to leave NiMH cells in any valuable equipment for very extended
periods of non-use, even the Eneloop types.
Your Radio Shack NiCd were likely damaged before they were stored.
Most of the circuitry in the old days were very simple. If you plug
external power into the CB walkie-talkie, the NiCd inside will
continually be charged, which will lead to excessive air pressure
inside because the electricity will start turning the water content in
the electrolyte into hydrogen and oxygen, and then the safety valve
will open to relieve the pressure, and from that point on the battery
will leak.
Sorry, but you're wrong. I never charged the NiCads in the walkie
talkie. They worked fine when they were last used and the battery
pack was not put away installed in the radio. The AA cells were
charged four at a time in external chargers because I wouldn't trust
*any* charger that charged any more than maybe two at a time in
series, let alone 8.
Most older battery chargers will not stop charging. You have to time
yourself to remove the the batteries from the charger after certain
number of hours of charging. That is the problem. Many people forget
and leave the charger on for days or weeks, or even months, so the
safety valve inside the battery will open up to avoid explosion, and
the batteries are ruined by continual leaks.
You're still wrong, but that won't count against you. Not in what
you said, but in the assumption that you made. :)
New charger these days have complicated circuitry to detect the fully-
charged state of the battery and stop the charging current. Some will
stop charging totally, but some will leave a "trickle charge" current
to top up the battery. The "trickle charge" current can ruin the
battery if you really leave it on for weeks or months.
Can, but not usually. It depends on the equipment. My old
cordless phones have very simple charge circuitry that never stops
trickle charging and I've only had to replace the battery packs
twice over the last 16 or 17 years. The original Sony NiCd battery
pack used very low capacity AA cells, and the most recent Radio
Shack replacement now uses much higher capacity NiMH cells inside
the pack, as the original battery pack is no longer available.
A normal alkaline AA battery does not have a safety valve because the
battery is not designed to be charged so it is built with a flimsy
casing. The battery will not explode but the electrolyte will simply
ooze out if you mistakenly charge it.
However, a NiMH or NiCd is designed to be charged, so that it is built
with a strong steel casing to withstand the air pressure from
electrolysis of water if the battery is charged to fast or too long,
and therefore a safety valve is necessary.
I have physically cut open some of the good ones and leaky one and I
can confirm that NiMH and NiCd do have a safety valve inside. Under
normal circumstances the valve is kept shut by a simply mechanism but
after the valve is pushed open it cannot return back to normal.
I'm well aware of the safety valves, but I also know from personal
experience that NiCd (and presumably NiMH) cells can and will leak,
even if leakage is much less common than with primary AA cells. The
really old Carbon Zinc (LeClanche) cells leaked corrosive ammonium
chloride quite easily. Alkaline-Manganese cells are much better,
but still leak, sometimes while they're still new, in unopened
packages many years before their expiration dates. I've never seen
or heard of lithium AA cells that have leaked but I suppose it's
possible, so I have no position on whether they can or can't. As
for the valves not being able to return to normal after opening,
you're wrong again, unless the cells you examined were sub-standard
or poorly designed. Energizer's NiCd Application Manual states that
the valves (and the cells) are only damaged if the valves undergo
frequent or extended venting. The NiMH Application Manual says :
Nickel-metal hydride cells contain a resealable safety vent built into
the top, as illustrated in Figure 6. The nickel-metal hydride cell is
designed so the oxygen recombination cycle described earlier is
capable of recombining gases formed during overcharge under
normal operating conditions, thus maintaining pressure equilibrium
within the cell. However, in cases of charger failure or improper
cell/charger design for the operating environment, it is possible that
oxygen, or even hydrogen, will be generated faster than it can be
recombined. In such cases the safety vent will open to reduce the pressure
and prevent cell rupture. The vent reseals once the pressure is relieved.
.
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- Re: Do NiMH batteries leak?
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- Re: Do NiMH batteries leak?
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- Do NiMH batteries leak?
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