My first response to any question about car batteries (12V lead acid) is that the answer to just about anything you want to know them can be found on one single website; Bill Darden’s most excellent “Car and Deep Cycle Battery FAQ”
The possible exception to that rule is the issue of the use of battery pulsators (sometimes referred to as “conditioners”) to restore old sulphated (sulfated) batteries, about which Bill Darden is cautious –as are we! However, as we do make use of car batteries occasionally as power sources in various projects, we did become interested in pulsators and bought one (very inexpensive) from a small company in Scotland http://www.courtiestown.co.uk/
Without doubt, the use of this device had a very beneficial use on older batteries whose performance had been degraded because of sulphation. This was a slow process, taking a couple of weeks, but for anyone considering using lead acid batteries for solar power storage, the use of a pulsators may be worthwhile.