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Date: Mon, 24 Jan 2011 07:57:11 -0500
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From: Brent Regan <brent@regandesigns.com>
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Subject: Re: Lithium Batteries
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Michael writes: <<<It seems there may be some discrepancies between 
theoretical extremes and real-world experience. Here's a link to one of 
the forums on which people are reporting on their results:>>>

I would caution that taking anecdotal "test" reports published on a blog 
as fact is a bit of a risk. Having a guy by the name of "Tostino" report 
he did a "few" discharge cycles with no observable imbalance tells us 
nothing. It certainly is not enough to contravene the battery 
manufacturer's published recommendations. How many cycles? What was the 
temperature? What was the rate of discharge and the depth of discharge? 
How was it measured? What was the rate of charge? What was the charge 
temperature? Did the discharge rate vary (like in an aircraft application)?

Hamid, on the other hand, has actually designed multi cell Li-ion and 
LiFePo power systems. One system was for Liquid Robotics 
http://liquidr.com and featured seven 6-cell packs that powered the 
electronics and payload of the Wave Glider (winner of the WSJ Innovation 
of the Year award). Photovoltaic panels were used to charge the 
batteries in sequence during sunlight hours. The prototypes we built for 
Liquid Robotics have logged thousands of charge - discharge cycles 
during several trans Pacific crossings and deployments from Baja to 
Alaska without any failures.

Reliability is, in part, the result of careful consideration of 
theoretical extremes. This frequently produces favorable real world 
experiences.

So, believe who you want, a guy who has 15 years experience designing 
scores of high reliability electromechanical systems including certified 
primary flight displays, Electronic Flight Bags and power systems for 
AUVs or a guy named Tostino you met online.

Oh, and here is another clue that implementing a Lithium battery power 
system is non-trivial; most cell manufacturers won't sell you the bare 
cells until they qualify your safety circuit.

Regards
Brent Regan