Lithium Ion hold significantly more charge than NiMH?

perfect... from manufacturers' point of view! =) expensive and need to
be replaced

 

Less energy? Most Li-ion batteries I've looked at (not many,
admittedly) are rated at less than 2500 mAh. Finding 2700 mAh NiMH
batteries is quite trivial.

--
Intaxication: Euphoria at getting a tax refund, which lasts until you
realize it was your money to start with.


/\ /\ /\ /
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mA-h does not tell the whole story. Time above a
usable voltage is also important.

Phil

 

It's impossible to compare Li-Ion with NiMH if you only have the
mAh rating, since no Li-Ion batteries supply 1.2 volts. But in many
cases (as you note) the Li-Ion batteries do provide less energy than
many people would guess. Here's an example.

The energy that batteries contain is roughly proportional to the
battery voltage * mAh, and multiplying them provides the capacity in
Watt Hours. As dpreview notes*¹, Canon's original 7.4 volt BP-511
battery had an 8 WattHour rating, and the improved BP-511A, used in
the G6 and 300D, due to its higher 1390 mAh capacity reaches 10.3
WattHours. In a weird move, Canon supplies their G7, 350D and the
new 400D with the smaller NB-2LH battery. It's 1.3 oz. lighter but
at only 720 mAh and 7.4 volts manages only a 5.3 WattHours. That's
a mighty poor tradeoff, especially for anyone that routinely carries
one or more spare NB-2LH batteries.

Compare this with a set of four 2700 mAh AA batteries, as used in
Canon's smaller A620/A630, which provide 4 * 1.2 * 2700 == 13
WattHours. This is 26% more energy than Canon's heftier BP-511A
provides, and 145% more energy than the NB-2LH.

*¹ http://www.dpreview.com/reviews/canong6/page4.asp

 

Yes, but at twice (or more) the weight. There are a lot of factors to
evaluate in choosing a battery. Also, cameras are designed to best use
a certain type of battery, and will usually work better with that
battery type.

 

Is it really "twice (or more) the weight"? Even if it is, saving
that extra 1.3 ounces is (as I said) a mighty poor tradeoff for
getting virtually double the battery life. I'll bet that if Canon
shaved off another ounce from their Li-Ion battery few would be
amused. And don't forget, the smaller the battery, the more likely
it is that the photographer will need to compensate by carrying
another battery or two, negating the reduced battery size and
raising the total amount of money sunk into batteries. Saving an
ounce can make sense for a small P&S, but even lightweight DSLRs
such as the 350D and 400D will often be used with lenses other than
the smallest, lightest fixed focal length or kit lenses and other
"stuff". Canon's decision to cut the battery capacity in half
brings to mind the familiar "penny wise and pound foolish". <g>

 

Yeah .. my take, too re the DSLRs. But maybe they
can sell more batteries that way ;-)

Phil

 

But LiIon cells are much higher voltage. Energy is volts times
amp-hours. A 900 mAh LiIon cell at 3.6 V is the same amount of energy
as a 2700 mAh NiMH cell at 1.2 V. Another way of looking at it: you
need 3 1.2 V NiMH cells to equal the energy of one LiIon cell if both
have the same mAh rating.

As a general rule, LiIon and NiMH actually store about the same amount
of energy per unit *volume*. LiIon is much better per unit *mass*,
since they are so much lighter than NiMH (and alkaline).

Dave

 

Thanks for the correction - I did not know they had different voltages.
My old Olympus took both, and so I assumed they had the same voltage.

--
As a child my family's menu consisted of two choices: "Take it, or leave
it."


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The Oly LiIon packs had two cells in parallel. That's why they were a
pack that slid in diagonally. The camera's regulators were good for
something like 4V to 9V so it could use 4-5V from four NiMh or the 6-8V
from 2 paris of LiIon.

 

??? Are you sure about this? If the Li-Ion cells were connected
in parallel they wouldn't be providing a voltage in that high 6-8V
range, but at a lower voltage comparable to what the four NiMH cells
could provide. Which camera(s) were they? DSLRs?

One way for cameras to more efficiently use alkaline batteries
would be to use circuits such as the ones used in Energizer's CHAA
and CH2AA chargers that use one or two lithium or alkaline AA
batteries and are used to recharge cell phones in the field.
Energizer claims "87% typical electronic converter efficiency" and
says that they can keep providing a 5 volt charging current even
when the AA cells have dropped to 0.6 volts. The single AA version
charges at up to a 320ma rate and the two AA version at up to 600ma.
Circuits such as these would allow cameras to get almost as many
shots from alkaline cells as from NiMH, where NiMH typically lasts 2
to 4 times longer than alkaline cells.

 

Four LiIon, two parallel pairs in series, is ~7.6 volts.

Watts = volts x amps

An alkaline battery always produces at about 1.5 volts. If you load it
down to 0.6V with a DC-DC inverter, there is 0.9 volts lost to heat
inside the battery. That's not very efficient.

You're talking about buffering alkalines with another storage device.
Ultra-capacitors can be used to improve the efficiency of alkaline
batteries but they take up space and cost money. There's little point
to using alkaline batteries plus ultra-capacitors together unless you're
over the current capability of NiMH too, which you aren't in a camera.
Buffering with ultra-capacitors is more for 2-way pagers where the power
source is a AAA cell, the average power draw is small compared to NiMH
self-discharge, and the transmitter needs short bursts of several watts.

 

Ok, that makes sense. But two parallel pairs is quite different
than "two cells in parallel". The only Oly battery I've seen is the
BLM-1 which is rated at 7.2 volts and as far as I can tell is
constructed using only two cells. You added "or the 6-8V
from 2 paris of LiIon" at the end of the paragraph, but it
conflicted with the earlier "two cells in parallel", hence my "???".

Obviously. In another recent reply I mentioned the similar energy
version, WattHours == Volts * AmpHours (giving examples using the
battery mAh ratings). Your reason for mentioning this is ... ???

Totally wrong. First, an alkaline "battery" contains more than
one cell. But that's a nit. An alkaline cell does not always
produce 1.5 volts. Fresh alkaline batteries can, if they're not
heavily loaded, causing an internal voltage drop due to internal
resistance. Second, Energizer's data sheets state that the
efficiency (and I quoted it) is 87%, which is extremely efficient.

You evidently have no idea what I was talking about. Where did
you imagine that anything was said about buffering alkalines? Check
the data sheets on Energizer's web site to see what their CHAA and
CH2AA charging devices are all about. They're intended to be used
in conjunction with Li-Ion powered cell phones, and can either
charge the cell phone's internal power pack or help power the cell
phone while it is being recharged. If anything can be considered to
be buffered, it's the cell phone's battery (often a single cell),
not the AA cells in the external charger which are buffering or
charging the cell phone. Ultra capacitors weren't mentioned and as
far as I can tell aren't used in Energizer's charging devices. Are
they in any way relevant? FWIW, the Energizer chargers are widely
available in many pharmacy/convenience stores, electronics/camera
stores, etc. The CH2AA sells for about $20 and includes a pair of
lithium AA cells. Join me in another several cups of coffee. You
appear to need a jolt of some caffeine.

 

My camera has a 3.7V 1150mA lithium ion cell. It is exactly the same
overall size as 3xAAA NiMH cells which give 3.6V & 900mA. So the lithium
ion gives about 25% more power, but costs 3 times as much. In my view the
litium ion thing is a rip off, and more camera manufacturers should provide
contacts for AAA as an alternative. Some cameras (eg. Ricoh GR) do give
this option so it is certainly viable, and a very useful backup.



--
_______________________________________________________

When you make your mark in the world, watch out for guys with erasers.
-- The Wall Street Journal
_______________________________________________________

 

Someone mentioned lithium ion being lighter than NiMH. Well I just put the
above batteries on the kitchen scales, not very accurate at this weight
range but the lithium are indeed a bit lighter, maybe 30g compared to about
40g for the NiMH. Not really worth bothering about unless your camera takes
a much bigger battery pack.


--
_______________________________________________________

When you make your mark in the world, watch out for guys with erasers.
-- The Wall Street Journal
_______________________________________________________

 

But Li AA cells are about 60% the wt of alkaline
AAs .. and last much, much longer.

Phil

 

Practical application. Lithium Energizer e2 AA's 400 to 500 shots and
they will not expire until long after my death. Very readily available
and reasonably priced.
OEM NiMH rechargable AA Batteries new, maybe ninety shots if your
lucky.
Aftermarket NiMH one year old maybe fifty shots if your lucky. Fairly
avalaible, not exorbitantly priced.
I do not use Li-Ion batteries in my still camera but I use them in my
video camera and my laptop, The biggest drawbacks I have found in them
is they're only good for about one year and then they discharge much to
rapidly and finding replacements at the corner drug store is not likely
to happen and they're incredibly expensive.
Turn off the LCD display and use the little viewfinder if you want to
maximize the number of shots you can take with a single charge.
The November 2006 edition of Wired Magazine has a good article on the
future of batteries.

 

That's less true than it used to be. Based on Energizer's data
sheets, their lithium L91 AA cells are rated at 3000 mAh, which they
indicate varies with load, but according to their Constant Current
Performance chart (with a single curve based on cutoff at 0.9v), the
3000 mAh appears to be pretty uniform at loads from 10ma to 1000ma.
From memory I think that Energizer rates their alkaline E91 AA cells
at 2850 mAh, but a similar chart on the E91's data sheet shows that
it supplies about 3000 mAh at a 10ma load, about 2400 at a 100ma
load and slightly less than 1000 mAh at a 1000ma load. Visual
interpolation was used since this chart doesn't have a curve for a
0.9v cutoff, but has three (1.2v, 1.0v and 0.8v). This indicates
that older cameras that were very power hungry could sometimes get
200% greater life using lithium AAs vs. alkalines. But the more
efficient recent cameras might only see a 20% to 50% advantage,
depending on the camera and how it is used. For very low drain
applications drawing less than 20ma, such as clocks, smoke alarms
and a few low power speakerless portable radios, lithium and
alkaline AA cells have virtually the same capacity. These values
assume reasonable temperatures of 21ºC. Performance at lower
temperatures is only shown for currents of 250ma, and at 0ºC,
lithium AA capacity appears to be reduced by about 2% to 3% but
alkaline loses considerably more, about 50% of its 21ºC capacity.

 

Are you talking about AA lithium cells? Those are about 1.6 V per cell.
But they are *not* lithium ion cells, and they are not rechargeable.

The problem is that there are about 5 different "lithium" chemistries in
use in consumer products, all with different characteristics, and most
of them are not rechargeable. So it's easy to confuse "Lithium Ion"
with any of the other lithium chemistry cells.

Dave

 

They were wrong. I have 2700 mAh cells for my Canon PS A620, and I
tried to wear the batteries out taking photos and have yet to succeed.


If you have a good set of NiMH cells and a decent charger, they'll take
you a long way.

30 - 40 shots maybe with Alkaline primaries . . .

At this point in the game, I've replaced my camera's 2700 mAh Sanyo
cells with the Sanyo Eneloop cells. While their capacity is rated @
2000 mAh, they're perfect because I don't use my camera every day, and
it's not uncommon for it to be put away for a week or 2 at a time.
(Sanyo claims the eneloops will retain 85% of their charge after 1 year
of non-use at reasonable room temperatures)

If I'm going to be doing heavy photo shooting (such as going on
vacation), I'll use the 2700 mAh cells because they pack more power but
have a higher self-discharge rate.