Well, I am learning a lot and have (as usual) learned myself into a corner. I was leaning toward an Amp/hour counter, like the Victron. (Am I right about that -- is that the main advantage of the Victron over the voltage-based monitors? I certainly want to know how many amp/hours I've got in the tank!)
But then I went to the Smartgauge site and started to plow my way through the article Don referenced above. And I came to this significant passage:
"The problem with traditional Ah or Coulomb counters is keeping them accurate. As batteries age their capacity changes, the charge efficiency changes as does the Peukert’s constant. A battery is an ever moving target, so the 100Ah battery you bought three years ago may now only be a 75Ah battery."
I'm going to ignore Prof. Peukert -- I only use one battery at a time. (I know, I know -- I am leaving money on the table by not using the batteries in parallel -- but I just like the rock-solid safety of using one and holding another as a spare, just in case.)
But the big problem is that I really don't know, and won't know, the true amp/hour capacity of my dumb lead-acid deep cycle battery. When it's brand-new, it's rated at 110 a/h, which means I can draw it down to about half of that without getting a pain in my anode (or whatever it is that happens when you over-discharge an old-school FLA battery).
But as the article points out, FLAs degrade over time, even when we baby them by never going below 12.1 volts (or 50% state of charge).
So that is now my question -- for those of you who are fans of Victron-type monitors, how do you deal with the problem of AHDS ("Amp/hour dwindle syndrome")?
That article goes on to say, by the way, that you can determine if your capacity is dwindling by conducting a 20 hour load test. The author says that no one really does that, in the real world.
My guess is that if you have lithium batteries, you don't have to worry about this phenomenon.
Bottom line -- if actual battery capacity is a moving target, then an amp/hour counter may provide a misleading over-estimate of the remaining juice. And if I have to indulge in guesswork, I can just whip out my cheap old-school multi-meter, measure the voltage, interpolate state of charge, and call it done!
Thanks again for all of the expert input - I know that this is a surprisingly touchy subject, and reasonable minds can differ about all of this. Battery care is both a science and an art!
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