A true amp hour counting battery monitor is hardly a necessity. It is a tool one can use to learn and to extend battery life, and notice when battery degradation is occurring, or when the battery is not getting fully charged, or if something is amiss.
If one is seeing the battery only drop to 12.5v by the morning, then they are skimming only the top 1/4 of their battery capacity, and it could be argued they have more battery capacity than they need. But that other 1/4 is filled with warm and fuzzies and there is no arguing against warm and fuzzies.
AH counting Battery monitors do complicate the wiring, when the alternator is involved as vehicle grounds need to run through the shunt.
My personal strategy is to cycle a single battery deeper, and I will go below 50%, as long as I know i have the means to 100% recharge the next day. A battery under 80% charged can basically accept huge charging currents, and huge currents can get a battery upto 80% charged quickly. So if those huge charging sources are available, I will make them work and work hard, in combination with whatever solar I have available.
Right now is cloudy, My battery monitor is displaying
12.8 volts
-0.6 amps
25 AH from full
and the 200 watts of solar at Noon is making 4.1 amps indicating I have 4.7 amps of loads running. Fridge and fans Tv and a few lights.
Now the battery newbie, who only has a panel display with green, yellow and red lights, would show a green light, and 12.8v, well that's fully charged right?
Well, no. Voltage in this case, and in most cases, when the other parameters are not known is misleading. My battery rested and fully charged is 13.06 volts, but more importantly I see that my monitor is saying I am 25AH from full. I can see that without the sun popping out, and without other other charging sources employed, that there is no chance for my battery to get near 100% by Sundown. First the sun would have to get my battery to 14.4v, and then be able to hold it there for about 4 hours as amps taper to 0.4 amps. It ain't gonna happen today. I'd need about 90 minutes of full sun to get it to 14.4v, and then about 4 hours more being held there before amps taper to 0.4. Even if I drive, well the battery once it gets to the 14.9v my vehicle allows, well it will not be requiring much more than 10 amps to be held there at this state of charge, even though my alternator could make 50 amps+.
Will I have enough battery power to make it through the night, yes, but I might take the battery to 40%, or less if I cannot sleep and stream movies..
If I do not employ other charging sources, the monitor might climb upto 10AH from full range, and the voltage will likely get to 14.2v at times, but the battery will not be fully charged, and once the sun goes down the voltage will be 0.2 to 0.3v lower than it would had it indeed reached full charge, as a starting point, and that is only 10Ah from full. Several days of only getting to 90%, and the battery just does not have that 90% to give, but somewhere well below that.
Part of this is post is to also show how misleading even the readings from a battery monitor can be. I do not trust mine as 100% accurate. It is all the numbers combined which then one can allow the interested or concerned human to interpolate the battery state of charge, or how close one can get to achieving 100%, and tailor their electrical consumption to stand the best chance of getting the battery to an actual 100%, and actual 100% is ~ 4 hours held at absorption voltage once it has been reached.
I do try and limit my electrical consumption in the morning so the solar can charge the battery at a higher rate.
Voltage is an important factor, but without knowing how that voltage is being affected by loads, charging sources, and battery age/degradation, it can be quite misleading. many people see anything over 12.8 volts and just assume the battery is full, or that all is well, but things can actually be far from it as far as the battery is concerned. But then again they are only batteries and who works for who?
When a battery is old and has lost capacity, voltage when charging rises faster than a newer battery that has not yet lost capacity.
So there is a lot of variables, and voltage when monitored often throughout many charge/discharge cycles can give the observer a general idea of where the battery actually is, but unless the observer actually cares, and takes into account the charging and loads on the system while charging, then voltage alone can mean very little and give a false sense of confidence. Also the observer needs to know when the battery is indeed full, and the blinking green light on a charge controller or other charging source does not indicate this. The Hydrometer will on a flooded battery, the ammeter will on an AGM battery, but voltage alone never will.
It is entirely possible to charge a battery, get it to rest at 12.8+ volts, but then dip the hydrometer and see 1.255 where as full is 1.275 or perhaps higher. The battery that gets to 1.275 Specific gravity on each recharge cycle will last more than twice as long as the battery that only gets to 1.260 each charge cycle. So If the person cares, then dip the hydrometer when the charge controller first drops to float voltage and blinks that soothing green light. Most of the time they will find the battery is NOT full, and more time at perhaps a higher absorption voltage is needed.
When the solar wattage is available but the charge controller cuts off the application of absorption voltage prematurely, well, that is a crime in my opinion.
With an AGM battery, the test of full is re applying absorption voltage and seeing how quickly the amps the battery can accept at that voltage taper to 0.5% of capacity, or 0.5 amps for a 100AH battery(20 hr rate). If I goose my AGM battery to 14.4v via my power supply, and it tapers to only 3 amps and holds there, I know this battery needs about 2 more hours at 14.4v. If it tapers to 0.9 amps then about 45 minutes to an hour. Often my battery monitor will already read 100% and 0AH from full, when the amps the battery can accept is still above this 0.5% threshold at absorption voltage, and the battery monitor is a liar.
So, one need not goto the same lengths as I do to get the battery to 100% charged as often as possible, my aim is to present what the battery Ideally wants for maximum longevity and the reader can then take steps to go as far as they want toward Ideal. Too many people think voltage is a reliable yard stick as to state of charge. If only it were that simple. If it were, then energy storage would not be an issue, but unfortunately lead acid batteries waste energy when charging, and degrade at a certain rate, and at a higher rate when they are not fully charged after each discharge cycle.
If one is consuming electricity when the solar is still charging the batteries, then it is better to be able to wait until after absorption voltage has been reached, as after that point the amps required to hold absorption voltage taper and the solar is making more energy than required to hold the battery at absorption voltage. This is why i try and limit my electrical consumption until absorption voltage is reached, and then afterwards I will plug in the laptop to charge, or turn the stereo up, or crank up the compressor fridge then lower it late afternoon. I don't like wasting solar, but after absorption voltage is reached, it goes to waste anyway. Since it requires time at absorption voltage, the battery cycler is better off the sooner in the day absorption voltage is reached. So more solar is better, better for the batteries and more convenient for the consumer of electricity.
TMG51, you looking for a front loading compressor fridge or a chest style?
