A battery isolator is a diode-based 1-way switch that allows charging current to flow into the batteries while preventing current from flowing back out. It keeps the more highly charged battery from discharging into the battery with lower charge. Battery isolators work best on two or more banks of similar batteries. Simple isolators cannot isolate a starting battery from a deep cycle house battery effectively. Either the starting battery will overcharge or else the house batteries might never fully charge. Which of these occurs will depend on which battery voltage the charging source is sensing. Some more intelligent isolators claim to avoid this problem. Another drawback of a battery isolator is that it presents about a 1-volt drop across its diodes, requiring the charging source to operate at a higher voltage for optimum charging.
