Question about the Noco Genius10 or any other really. At what voltage does a "smart charger" consider a typical lead acid group 24 battery fully charged?
I ask because I've been charging a 24F marine type battery used on my gate opener for two days with a Genius10, voltage is 14.2 right now, and the green light continues to slowly blink.
Voltage-based SOC determination is really only relevant at open circuit (OCV) (nothing connected, nothing loading it or charging it). Getting a true OCV is a hassle in practice, so we usually just apply the meter to the battery and check with everything turned off, and hope that the minimal load that is always there isnt enough to sway it much. Usually its not.
Chargers apply some variant of constant current and constant voltage, with cutoff voltages based upon a variety of factors. An example is to charge a battery at constant current (say 10A for your NOCO Genius 10) until the battery voltage hits 14.7V, and then hold a constant voltage at 14.7 until the current accepted by the battery reaches some level.
In theory, the low current level reached that indicates full charge is based upon ampere-hours of the battery... Which is often not provided on car batteries. In theory, the end of charge is when, say, 0.05*Ah is flowing in at 14.7V. Note we dont tell chargers the Ah of our batteries. So its usually some arbitrary number.
Thus you can kind of tell by a few things:
1) Specific gravity of electrolyte (the real test as it tells you what the chemistry is doing)
2) OCV if the battery is sitting stagnant
3) A fraction of the Ah rating of the battery if it is undergoing charge
UPDATE: Well looks like it finally reached battery nirvana. The Noco's green light is steady. My mistake was buying a Marine Starting battery from Walmart two years ago. I did not know at the time there are Marine Starting batteries, "MS" and Marine Deep Cycle batteries"DC". I grabbed the first battery with "Marine" on the label. It was about $20 cheaper than the next one up, a Deep Cycle. My application is in a gate opener charging from a solar panel (when the sunlight is bright enough) so it needs good reserve power and able to take deep discharging during dark dreary days. Originally it came with an Interstate Deep Cycle Marine battery, 20+ years ago. It lasted about 4 years. The unregulated solar panel voltage gradually boiled the battery dry and it failed. I added a regulator circuit and next battery, a 100 AH SLA AGM big orange beast originally used in cell tower backup power I bought at a ham radio sidewalk sale, which lasted 14 years. Was sad to see it go. A similar battery now is way out of my price range for new and I haven't seen surplus batteries like that in years.
As I recall, the NOCO units swap back and forth between blinking and solid. And it pulses green in two different ways (duration and rapidness of pulses). My take is that when it is doing the CC portion of the charge, the red and yellow lights are on based upon what fraction of the maximum charge current is currently reached (as a proxy for how the battery is changing and SOC is increasing. Again, it has no real way to know % SOC, because it doesnt know the nameplate Ah capacity, or how degraded the battery is. After some period of time above a setpoint voltage and low current, it changes to a pulsing green. When the provided current is below some fraction of an amp, and voltage is above a certain level, it goes solid green to indicate full charge. Im not sure why my 2A unit doesnt hold a CV charge for some period. After sitting with the power supply on at that low level for some period, and the solid green light lit, it then turns off the power supply (so for example it might go from a tiny fraction of an amp to zero), and it just monitors the battery voltage as an OCV-type measurement. Once the measured voltage goes below a certain level, it will re-initiate at least the last part of the charging profile.
Recall the noco plot from the first page.
I suspect that the red and orange are some of the blue peaks where upon hitting a voltage, it ratchets down the current... It creeps up on max voltage, which is somewhat low for battery charging, but safe, multiple times, all in CC mode.