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Old 25-10-2006, 08:48   #1

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Toyota on Lithium Deep Cycle Batteries

"A crucial problem is that the Prius battery will last well over 100,000 miles, but only because it is babied. It is seldom charged above 60 percent of capacity, or allowed to fall below 40 percent. If it were charged fully and allowed to run down, like a laptop battery, it would, over hundreds of cycles, lose its ability to hold a charge, Toyota says. That suggests a replacement cost in the thousands of dollars. "

Interesting comment from Toyota, about the special problems connected with Lithium-based deep cycle batteries. For those of you who have wondered when boats might get "new" battery technology with more power density than lead acid...I guess the answer is "Not right for us."

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Old 25-10-2006, 11:41   #2
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Hmmmmm, wonder why only 60% full charge. You would think they would make the 60% part the full charge limit and anything above that over charged. I mean, they must surely have a special charger for these right??


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Old 25-10-2006, 11:53   #3

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Special charger? Ya, a complete energy management system that also controls charging, custom built all the way.

Makes no sense to me either, but that's what they are quoted as saying.
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Old 28-10-2006, 11:47   #4
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Lithium-ion battery charging/cycling

When charged to a maximum "full" state lithium-ion batteries are driven to 4.2V per cell. Near that voltage there begins a plating out of lithium at the anode which can oxidize and vent with some danger of fire and/or explosion, given sufficient material, time, and temperature.

When discharged to 1.25 Volts per cell there is a danger of copper dendrite formation between the anode and cathode, again giving rise to potential instability when recharged...not safe.

When cycled between levels about 3.95 Volts per cell and 1.3 Volts per cell one gains reliability yet does not optimize the number of likely cycles for greatest life. Somewhere between the approximate "safe" cycling over an 80% dynamic range (versus the not-so-safe potential 100% rating) and a high cycle life of a 60% dynamic range is the optimum cost per cycle over life dynamic range.

I believe that the article misinterpreted such specifications to state incorectly that the battery is only charged to a 60% state-of-charge instead of correctly stating that a 60% dynamic range as compared to a possible 100% dynamic range. With a 60% dynamic range usage the battery is charged to around an 80% or up to 90% state-of-charge depending upon the "safe" reserve allowed at the lower end to accommodate self-discharge for sufficiently long periods without dendrite formation.
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Old 28-10-2006, 14:00   #5
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YEAH Rick! Thanks for that great explaination.
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