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<HTML><HEAD><TITLE>Re: [RE-wrenches] discharging Rolls batteries</TITLE>
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<DIV>Capacity is reduced at low temperatures. Now does this mean that
there really is less energy in the battery, so that if I take out 50% of this
reduced capacity I will only end up with a 50% state of charge once it has
warmed, or is this just a performance hit that reduces the voltage and makes
the battery capacity appear to be less? Will the battery actually have
less amphours to deliver, or will it just be delivering at a lower
voltage? My point is to ask whether it is legitimate to push the battery
to a lower voltage in cold weather on the assumption that it is not really
running that low, but just sluggish with cold?</DIV></BLOCKQUOTE>
<DIV><FONT face=Arial size=2>Hi Hugh, When discussing battery characteristics
with a chemist at my supplier years ago I was told the capacity at 0 deg c is
around 50% of that at 25 deg c because the ion transfer rate within the cell is
slowed by the low temperature. This "loss" of capacity is recovered once
the battery warms again. The same reason why a fully
charged cranking battery in a car can fail to turn the motor in cold
weather. Ion rate is so low it simply can't deliver enough current to the
starter motor.</FONT></DIV>
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<DIV><FONT face=Arial size=2>So, the answer to the second part of your question
is yes.</FONT></DIV>
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<DIV><FONT face=Arial size=2>A good thread with lots of useful background into
how batteries really operate.</FONT></DIV>
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<DIV><FONT face=Arial size=2>Bruce Geddes</FONT></DIV>
<DIV><FONT face=Arial size=2>PowerOn (at the other end of the
world)</FONT></DIV>
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