MS's great tutorial notwithstanding, I have a basic question re battery monitors in general, particularly the "state of charge" function, common to all brands I know of.
I understand (I think) that in order to ascertain how much charge is left in a battery bank...starting from a fully charged battery or bank, one must tell the monitor how big the battery was in the first place...similar to the way the gas gauge works in your car...if you didn't know how much gas the tank could hold, how would you determine when it was half full, for instance.
So suppose you had a house bank of 200 AH. That's the capacity of "the tank" you would program into the monitor and, as energy is consumed, SOC would diminish accordingly and all be well. But what if you decide somewhere along the way you wanted to switch another battery into (or out) of your bank via the 1-2-B switch.
I have a client who does just that. He has a two-battery house bank, a start battery, and an "at large" battery which can be dedicated (by switch) to either house or start function. He likes the sense of redundancy he says this configuration gives him. He makes his decision, where to put the orphan battery, based on the SOC he reads from his monitor.
He brought the boat in complaining that his batteries were unreliable...says his system works all the time that way and there's something wrong with his monitor and would I replace it...and his batteries.
If monitoring a "bank" the bank should be one bank with no ability to switch batteries on or out. If you do you've just royally screwed up the calculations the monitor is doing and made it all but useless.
Your client would be MUCH better served to apply his "at large" batteries to the house bank 100% of the time, hard wired, without a switch.
However, and this is the big "BUT", as he is using them the batteries will all now be at odd stages of life. The house bank could have 200 cycles to 50% on them and the "at large" only 20 cycles. Permanently combining these is not necessarily the best idea as the good batteries will be out of balance with the used batteries. Banks shoudl ideally be of the same exact battery, purchased at the same time and of the same date code. I actually take it one step further and use my expensive battery analyzer to match CCA when I buy batteries. Just bought two banks for customers in the last week and went though 13 batteries to get 3 matched batteries and two matched batteries.
I also print out a receipt from my analyzer so we have a reference baseline and something to compare to in the future.
The easiest way to get the most life out of a bank is; the biggest bank possible at the lowest possible discharge levels
Your customer is actually doing himself a big disservice by using "at will" batts and it shows his lack of understanding. He ideally needs to listen to you and let you be the expert but I have customers like that too and they eventually do listen after their "great idea" backfires..
Your customers monitor is not the problem your customer and his lack of understanding are causing the problem. You CAN NOT use a monitor accurately they way he is trying to..