If you have wet lead acid batteries and a three phase charger, then to charge a battery fully, you need to run through bulk, then absorption phase.
Bulk phase will depend primarily on the state of discharge of your batteries, the power of the alternators and the current that you are drawing at the time - which obviously reduces the current available for charging. Absorption phase varies a bit with battery size and the length of time of the bulk charge, but about three hours is par for the course. If you really want to take care of your batteries, then you will occasionally (ideally a couple of times a month) run an equalisation phase - in the submarine world known as "gassing the batteries". Net result is at least six hours plus including equalisation. Few people do this, and doing it on the diesel almost certainly is economic nonsense. The common way rarely includes equalisation, and for leisure batteries this is probably the sensible option, balancing engine wear and running costs against the resultant shorter battery life. Determination of the time to move from one phase to the next is largely based on voltage. My own experience is that I rarely do more than bulk charge with the diesel, and call into marina to do a full charge. My bank is bigger than most - for a bank of 500 or 600 amp hours (or less), again, it probably makes sense just to accept the resultant shorter battery life. Starter batteries have a different design, and will deliver a very high current for a very short time only. Fully charging them will happen well within the time needed to charge your domestic batteries. Down side of start batteries is that they are very intolerant of deep discharge - hence the practical problem that most of have experienced at least once in our motoring lives - if your battery ends up completely dead, your incidence of problems with it increases significantly until you finally give in and replace it. The curtis instruments site has a battery textbook that will tell you all you want to know about batteries and charging, and a whole lot more. http://evbatterymonitoring.com/WebHelp/Battery_Book.htm#Section_3.htm If this link gets messed about, put Curtis Instruments in to google, and you will get it. Section three deals with charging. Regards Charley Felonious Mongoose
