glider battery duration problems

Dave Springford wrote, On 10/2/2013 5:57 PM:
I guess it depends on how one defines capacity. If you take it as
voltage drop from 12V then it is probably the 3% value that you use.
If you take it as the battery's ability to do work and the SLA stops
doing useful work at 10 V, then you have a 2V range from which the
percentage is calculated resulting in the larger drop I quote.

Of course, the thing about statistics is that they will tell you
whatever you want if you torture them long enough.

Capacity is defined as amp hours (sometimes energy is used). It is
definitely not defined as voltage or voltage lost, though measuring
"standing" voltage is one way to estimate the state of charge. Fully
charge an SLA battery, let it sit for a month at 68 deg F, measure the
amp hours, and they will be about 3% less than if you had measured them
right after charging. That means an 8 amp hour battery loses about 0.24
amp hours a month. The voltage will also fall during the month,
approximately 3% of that two volt working range, or about 0.05 volts.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)