Originally Posted by barnakiel
Why not just have a look at the voltage?
I would guess that when a battery is neither charged nor discharged and has been sitting like this for a moment, the voltage corresponds to the state of charge.
In the old days, we did go by v, for lack of a better system. In fact, reading the specific gravity of a wet battery, (each cells averaged out #) was a rather accurate way, but WAY too much hassle!
Voltage is EXTREMELY inaccurate as far as knowing a batteries state of charge. If no juice went in or out for half a day, then a v reading of 12.6 is a full "wet" battery. The thing is, that this RESTED BATTERY is hard to do, while living on the boat, and a v of 12.4 is quite low. The sensor line losses, and analog meeter's inaccuracies, make this useful only to know if the battery has some charge or not. It won't tell much more.
The "Link 10" and their cousins, have a shunt in the NEG house bank wire. Attached to the shunt, (and + side), are sensor wires that run to the Link 10s little computer brain. Once you teach the computer the batteries capacity and type, then top off the battery, it counts the amps going in or out with astounding accuracy, to the tenth of an amp! It re-zeros itself every day after topping off the battery bank to 100%. They're the cats meow!