T&T: Battery temperature

[capteric36 at sbcglobal.net]

 Hi All,
 According to Concord  (the manufacturers of the
AGM batteries I use) there IS a reduction in
battery capacity when the temperature drops.
 On their website they provide some curves to help
determine various factors regarding battery
performance and charging.
 As the battery temperature increases the charging
voltage must be lowered, as the battery
temperature goes down the charging voltage must be
raised.
 The amp hour capacity of the battery is reduced
as the temperature goes down.
 On their curve it shows that at 30 degrees C the
capacity is about 100%.
 At 20 degrees C the capacity is reduced to about
95%.
Thus there is about a 5% reduction in capacity
(this is NOT a linear curve, the following is only
an approximation) for each 18 degrees F reduction
in battery temperature.

 The XBM (Xantrex Battery Monitor) offers an
optional temperature sensor to allow for a more
accurate 'prediction' of time remaining at 'the
current level of discharge' before recharging
would become needed.
 It is also noted that battery capacity is rated
at a battery temperature of 77 degrees F, thus a
battery at 50 degrees F would have a capacity
reduced by MORE  than 5%.
 I hope this helps somebody.

Eric Thompson
S/V Procrastinator
South San Francisco
capteric36 at sbcglobal.net