Car repair shops will put additional charges if you have them install the second battery. Some have purchased one of these and it carries out great. However, we don’t use it the way it should be used. The normal way is to charge the deep cycle batteries from the bus alternator. What I do is I charge the car battery from the solar panels. This way, the battery will still charge if there is enough sunlight, even if my deep cycle batteries are drained. This is quite possible as the bus is often immobile, making the bus battery drain.
I believe that present battery isolator is better compared to continuous duty solenoid as it has a few edges over the latter. For instance, when using a CD solenoid, the two batteries are connected when you start the engine. Thus, if the house battery is drained, and the starter battery is a little flattened, the house battery will automatically equalize with your starter battery, at a voltage which is below what you need to start the ignition. To avoid this, you would need to start the engine right away.
Secondly, using the smart start (how to install battery isolator guide) will help minimize the power fluctuations that happen when starting the engine. These power fluctuations occur since the engine needs 13.2 voltages to power up. However, the starter engine is normally below that point, so the alternator has to power up the starter engine.
For second batteries, I suggest you buy a deep cycle battery with around 80 amp hours, or a maximum of 135 amp hours. If you want a much higher size, you must make sure that the deep cycle batteries are properly charged at all times. The logic behind this is that larger-sized batteries needs more time to charge. Thus, if you will not be driving for many hours every day, your deep cycle battery will easily drain, and eventually, it will have a shorter life span.
Having a battery isolator will also protect your deep cycle battery from power fluctuations when starting your car. Here is how it works.
Normally, your car alternator charges one battery. However, you can definitely install a second dual battery. It’s easy to do, and all you need are a few cables. But this means that your alternator will charge both at the same time. Furthermore, when the primary battery is drained, your second battery is also drained. If you have a battery isolator, things will be different.
A battery isolator works like an automatic control switch, allowing the second battery to charge only after the first battery is charged (or has reached a voltage of usually 13.8 volts). Both batteries will then charge until the voltage of the first battery goes below 12.7 volts on a 12-volt system. The isolator will then automatically disconnect the first and the second battery. Thus, when the first battery is below 12.7 volts, your power source will be the second battery only, not the first battery since they have been disconnected already. Through this system, your car battery will not be drained such that even if your second battery does drain, you can still start the engine of your car.
If you examine the diagram on the site of dfna, you will see that its has layout of a basic dual battery isolator wiring diagram. On the left side is the car battery which is charged by the alternator. In the center is the isolator; while on the right is the second battery. The illustration, however, does not show the two fuses required to be mounted on the positive (red) wire. The isolator acts as a switch (red wire) that automatically permits current to flow from the car to the second battery when the first battery is completely charged.