12v Battery bank set up in parallel with balanced draw

12v - 620Ah (155 Ah * 4) AGM (absorbed glass mat) sealed battery bank in parallel manufactured by Vmaxtanks and set up by yours truly.

These batteries have exceeded my expectations thus far and I cannot wait to get them set up with my RV solar charger and load distribution system. Testing in the video shows a full battery bank even after being at rest in sub zero temperatures for months. 12.73 volts is a full battery at rest for my batteries. A battery at rest should be left without charge or discharge for roughly an hour.

A note on battery chargers, make sure you understand some basic battery engineering. Average 12v batteries generally require 14.4 to 14.8 charging voltage (call your battery manufacturer). Check your battery charger's charging voltage by using a DMM while in operation. Many chargers are only reaching 13.2 to 13.8 and this will never get your batteries to full, regardless of what your idiot light tells you. Batteries need to have the proper charging voltage applied until the batteries themselves reach that voltage, and then hold that voltage for several hours before they are fully charged. Do some research, and set yourself up properly, or else you are not getting full potential out of your 12v system.

A note on battery monitors. This is another place where the industry lets us down. Cheap battery monitors such as the idiot lights in expensive RV's are generally hooked up somewhere in the wiring of your electrical system rather then directly to your batteries. Not only does this not account for the voltage drop problems in DC systems but also does not account for the voltage difference when charging and discharging. Be aware that many of these battery monitors are set to full at 13._ volts and as discussed this is not a full battery. these two issues with common battery monitors mean that many people are unknowingly destroying there batteries by only charging them to 55% to 70%. Ask yourself who profits from these issues? Certainly not the consumer.

The best way to check your battery level is physically, by opening it up and checking the fluid density with a hydrometer (10 bucks at an auto part store). This works great for standard lead acid batteries which is cost effectively the best way to go. I have my batteries indoors so must use sealed AGM batteries, no way to use a hydrometer on this set up. I must rely on DMM's and a microprocessor digital battery monitor for decently reliable readings.

A great link to related information on real 12 volt tips from an engineering perspective, not a sales pitch:
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