On 14/12/2016 16:01, charles wrote:

You certainly can isolate batteries via diodes. Lucas used to make a unit
-about the same size as an ignition coil specifially for this purpose. Our
tecnical survey vehicles used them in the 70's and '80s. After then, a
hefty relay, which closed when the alternator was producing enough volts
was used.

You can isolate them, but the voltage drop greatly reduces the charge
rate, and it will taper to zero before the battery is anything like
fully charged.

Bill