Re: Lithium-Ion RCR-V3 Batteries?

From: Searching_ut (Searching_ut-nospam-_at_sprynet.com)
Date: 02/16/05 

Date: Wed, 16 Feb 2005 01:17:56 GMT

For the most part, I too prefer the NiMh. However, In an environment like a
laptop computer where you can expect the battery to be subjected to fairly
high temperatures for long periods of time, I prefer NiCd batteries because
they tend to be considerably less sensitive to heat over time. As for the
environmental concerns, I've found batteries pretty easy to re-cycle in my
area. I have a batteries plus just down the road that will take them no
problem.

As for the cell imbalance problems, that does tend to be a problem with pack
type batteries, be it lithium or Nickel you're using in your laptop. That
said, the problem generally can be minimized or eliminated by using battery
conditioners once a month or so that discharge the pack down, then re-charge
using a slow (1/10c or slower) trickle charge rather than a peak detection
method. (cell balance is more complicated with lithiums) I would think it
easier and cheaper for laptop manufactures to build in circuits to keep NiMh
or Nicad packs conditioned than it is to build the charging/monitoring
circuits to prevent cell imbalance, over/under charge/discharge etc
necessary with Lithiums. For the cell phones, and other devices that only
need 3 volts or so, the problem would however be completely eliminated,
which is a very good point.

As for the initial posting, I was curious to how the new RCR-V3 lithiums
might compare to AA NiMh, so I did a quick and dirty cap check on some
batteries I have available. Using a Triton Hobby battery
charger/discharger/conditioner, I discharged a 7.4 volt 1300 mAh lithium
battery that I have for my Cannon digital camera at a constant current of
1.3 amps, while logging the batteries voltage using a RS232 interface
capable digital multimeter. (Capacity wise, the camera battery appears to
basically be a two cell series version of the RCR-V3). Using the average
voltage I obtained during the discharge for the math, a 6 volt cutoff for
the test, and the amount of time the battery was able to supply the current,
I came up with a single cell battery capable of around 3.46 watt hours if it
has half the power available as the two cell camera battery. (It's about 7
months old, maybe a couple dozen rechargings)

Next I did the same capacity test on a 2000 mAh Rayovac AA battery I've had
for a couple years which has been charged up well over a hundred times using
a 15 minute charger. Allowing the battery to become fully charged by leaving
in the charger a couple hours I set up a 2 amp discharge rate (1C again) and
a 1 volt cutoff. With the results, I came up with a Watt hour rating of 3.64
watt hours for a pair of the rayovacs. Assuming the circuit was designed to
be compatible with the lower voltage of a pair of AA NiMh batteries, I would
expect better performance with AA NiMh batteries based on what I saw during
the capacity test.

While I would really need to make a couple improvements to my test
proceedure, and compare an actual RCR-V3 rather than just a representative
Lithium battery to make the test worthwhile, it does tend to support my wild
guesses that the lithium AA replacement wouldn't provide any significant
benefits for my uses in areas where I now use AA batteries. Couple the
marginal if any benefit with the high cost and they don't appear very
attractive to me.

For what it's worth.

Jeff

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