On Tuesday 13 May 2003 16:08, Brian Densmore wrote:
> I think perhaps the 10% should have been
> more like 1%, or .10%, but I'd still like to know the source of this
> data.
>
> Brian

Lead-Acid Batteries by Richard Perez (Home Power Magazine) - 
http://www.homepower.com/files/hp1-25.pdf

Self-Discharge Rate vs. Temperature

All lead-acid batteries, regardless of type, will discharge themselves over 
a period of time. This energy is lost; it is not available for our use. The 
rate of self-discharge depends primarily on the battery's temperature. If 
the battery is stored at temperatures above 120° F., it will totally 
discharge itself in 4 weeks. At room temperatures, the battery will lose 
about 6% of its capacity weekly and be discharged in about 16 weeks. The 
rate of self-discharge increases with the battery's age. Due to 
self-discharge, it is not efficient to store energy in lead-acid batteries 
for periods longer than 3 weeks. Yes, it is possible to have too many 
batteries. If you're not cycling your batteries at least every 3 weeks, 
then you're wasting energy.

If an active battery is to be stored, make sure it is first fully charged 
and then place it in a cool place. Temperatures around 35° F. to 40° F. are 
ideal for inactive battery storage. The low temperature slows the rate of 
self-discharge. Be sure to warm the battery up and recharge it before using 
it. nature of chemical batteries most manufacturers do not guarantee them 
for long periods of time. On a brighter note, we have discovered that 
batteries which are treated with tender love and care can last twice as 
long as the manufacturer's claims. If you're using batteries, it really 
pays to know how to treat them. Battery Maintenance There is more to 
battery care than keeping their tops clean. Maintenance begins with proper 
cycling. The two basic decisions are when to charge and when to stop 
charging. Begin to recharge the battery when it reaches a 20% state of 
charge or before. Recharge it until it is full. Both these decisions can be 
made on voltage measurement and the information on Figures 1 and 2. These 
rules apply to deep cycle lead-acid batteries used in deep cycle service.