Hi again DL, just about all DC/DC manufacturers state to only use similar battery types with their DC/DC device.

The reason for this is that to get an advantage from their device, you set the device to charge a specific type of battery and this then allows the device to TOP OFF that type of battery using the maximum safe voltage that that specific battery type can be charged at. Allowing the battery to be TOPPED OFF quicker that what some alternators can do.

This is one of the few advantages a DC/DC device can offer over charging with an alternator, but the draw back is that all the batteries must be of the same type, or you can damage one or more of the batteries by over charging them.

As posted earlier, this is not a situation that occurs when charging with an alternator.