Of lot of interesting links. Of course, none are relevant to the discussion.
For example, much of it refers to SLA batteries, what here in the States are
usually called Gel batteries. Admittedly, their "open circuit voltage" is
higher: 13.0 Volts is considered 100% charged, and 12.6 would be roughly half
discharged. Further, the settling time is considerably longer.

However, for a normal flooded battery an open circuit Voltage of over 12.6 to
12.8 (depending on the model) implies 100% charged. As Nigel Calder says "If
Voltage readings are to be a meaningful reflection of the state of charge, the
battery must be allowed to sit for at least 10 minutes; and hour or two would be
better, overnight would be best (gel-cell batteries may to 48 hours to
stabilize)." He then refers to a chart that indicates 100% charged for 12.6
Volts or greater (typical wet-cell);13.0 (Gel-Cell).

A fuller description at:
http://www.optimabattery.freeserve.c...AQ/carfaq4.htm
where it explains that "Surface charge is the uneven mixture of sulfuric acid
and water along the surface of the plates as a result of charging or
discharging. It will make a weak battery appear good or a good battery appear
bad." In other words, of you read the Voltage immediately after removing the
charger, you will be misled as to the state of charge.

You mentioned you have Rolls Batteries. Here's their service bulletin, where
they say "Determining state of charge by voltage is more difficult as there must
be no load or surface voltage present", but they indicate 100% charged is at
12.6 Volts:

http://www.rollsbattery.com/Bulletins/600.htm



"Gould 0738" wrote in message
...
An SLA must always be stored in a charged state. A topping charge should be
applied every six months (or other time intervals as recommended by the
manufacturer) to avoid the voltage from dropping below 2.10 volts per cell.

An approximate charge-level indication can be obtained by measuring the open
terminal voltage of the cell while in storage. A voltage of 2.11V reveals that
the cell has a charge of 50% and higher. If the voltage is at or above this
threshold, the battery is in good condition and only needs a full charge cycle
prior to use. If the voltage drops below 2.10V, several discharge/charge
cycles
may be required to bring the battery to full performance.

(from)

http://www.allegromicro.com/techpub2.../index3311.htm

*******************

2.11 volts per cell indicates as little as a 50% charge, according to this
source