Recently I had both batteries on my Chevrolet Silverado 3500 Dually Diesel tow pig die at about the same time. One battery dropped to 4 usable volts, and the other was 12 volts with 59 cold cranking amps. The truck would not start, and if it was jump started it would not function correctly due to low voltage on the electric system. I purchased and installed 2 new 1000 cold cranking amp batteries which woke the truck back up. I’m not sure I have ever heard the starter spin as fast as that initial hit with the new batteries.
The truck is not driven very often so I had a fear of the batteries taking another nose dive with large voltage fluctuations between starts of the truck. I decided to plan and implement a solar charging/conditioning solution to keep the batteries healthy as long as possible. The initial plan was to put a small 10 watt solar panel trickle charger on the batteries, but the customer reviews on those solutions did not prove to have long life. I began to look at the higher watt, longer life solar panels that are hard mounted and supply up to 30 watts of power. This type of wattage would supply enough power to actually charge a battery to full charge in about 2 hours. One of the downfalls of that much power from a solar cell to a battery is the need to insert a charging circuit that will control the amperage and duration of charge for the battery. I was able to find just the solution from Allto Solar. The Charge MPPT keeps track of the connected battery voltage and the connected solar panel charge ability and changes from charge to condition on the fly.
This type of solar panel charging solution is not recommended for use while the vehicle engine is running and the alternator is charging. I will remedy this suggestion with a relay that will interrupt the battery connected charging ground wire with a relay connected to the ignition switch. When the truck key is turned to the ignition on position, a relay will be triggered to disconnect the ground signal to the MPPT charge conditioner and allow the alternator to take over the charging duties. In the near future I will also add a photocell that will disconnect the solar panel charge solution at dusk since it will no longer be effective. When the sun comes back up at dawn the solar charging circuit will be reactivated. This process will be handled with a relay that will also interrupt the ground signal to the charge conditioning circuit in the MPPT. This sun sensing solution will also become active if the truck is ever placed in a storage facility or put in the shop for repairs. In that case I will switch to 120v charge conditioning using another solution if it becomes long term storage.