We have monitoring sites consisting of a CR1000 whose power source is a 12V Genesis battery that is charged through 2 solar panels and a CH100 solar regulator. We have had to replace the battery when it's charge dropped below 8V, and we recharge these batteries with a solar panel connected to a CH100.
The batteries have been kept on the charger in direct sunlight for many hours, however their charge will not go above about 10.5V. I have used a voltmeter to check the charge coming out of the CH100 and it is a little over 13V. The batteries also seem to discharge fairly quickly, even when not in use (from 10.5V to 9.5V in a 24 hour period).
The lowest the charges get on the batteries is around 7V or 8V, and I do not believe this is low enough to damage the batteries.
Has anyone had this problem before or know of a solution?
Assuming the batteries are lead-acid, they consist of 6 cells each with a nominal voltage of about 2.1V, and it sounds like yours have one bad cell. 7 or 8V is extremely low, and it wouldn't surprise me to see permanent damage. We've sometimes seen bad batteries recover to some extent, and tend to see jumps of about 2.1V up or down.
Depending on priorities and the type of equipment you're powering, it may be possible to monitor the voltage using the datalogger and turn on/off high loads using the SW12V relay or equivalent, and so aim to prevent discharging the batteries to such an extent.