When one puts a smart charger on a battery at a high state of charge, it can decide to do all sorts of things.
The Noco genius 1 I tested, had three different amperage levels on the agm setting.
going by memory here:
It would output 1 amp until 1 ampere got the battery upto 13.6vish, then only 0.5 amps until it reached 13.8v, then 0.25 amps to get the battery to 14.7v. Once it hit 14.7v, it quit outputing any amperage, and would not start again until battery voltage was drawn down to 12.69v.
It can take days for this surface charge voltage, to dissipate when disconnected from anything, or when in vehicle, for parasitic loads AND self discharge to btrng it down to 12.69v . Temperature and battery health are huge influencing variables as to how long it takes surface charge voltage to dissipate, after the charger stops..
One mighty see 12.83v, and this is NOT the float voltage, the noco is likely just waiting for battery voltage to fall to 12.69v before it starts putting out amperage again and then will again raise the battery voltage to the 3 setpoints it is programmed to seek.
I've no Idea if the genius 10 does something similar, on the agm setting.
You tell me.
When the smart charger quickly is able to raise battery voltage high, it assumes the battery is very close to, or at full charge ,and will perhaps just get it to mid 14,s then stop entirely, waiting for battery voltage to drop.
Some chargers seeing a low current quickly raise battery voltgae, might then skip pas bulk and absorption stages, and instead go right to float mode, and output enough amperage to only hold the battery at the programmed float voltage.
Idea float voltage is temperature dependent and battery specific.
The Noco genius one strategy in terms of just shutting off after achieving 14.7v, rather than holding the battery at as set float voltage can be a good thing. or not so good.
Takes for example my Northstar AGM. This battery fully charged holds 13.06v for weeks, when not connected to anything.
If the Genius 1 waited until its voltage fell to 12.69v, it would take months and the battery drained to 85% or so before it kicked back on.
Note, i did not wait, to test to see if there is a time trigger on the Genius 1.. I was loading the battery with some 12v LEDS upto about 1.5 amps iirc, and only when they drew it down to 12.69v did the Noco genius one kick back on and seek 13.6+v again
One size fits all Fload voltages on a battery well outside of 77f or one specifying high or lower float voltage is not even close to ideal. No matter how nice the word 'trickle' apparently sounds.
Too low a float voltage on a cold battery will allow it to slowly discharge and sulfate, too high a float voltage will eventually overcharge. use water, positive plate corrosion. premature failure.
Tricking smart chargers into doing what one is expecting, often requires draining the battery a fair amount, so that the charger can then put out its maximum amperage and slowly raise the battery voltage from low 12's, to mid 14's, then holding it mid 14's for x amount of time.
I got so sick of trying to second guess smart chargers, I now just use a adjustable voltage power supply, and watch an ammeter.
Voltage is electrical pressure
The battery decides how much amperage it can accept at the voltage/pressure reaching the battery terminals.
If the charger is rated for 10 amps, and placed on a well depleted healthy battery, it should initially provide 10 amps until the pressure rises to mid 14's.
A 100 amp hour healthy, battery drained to 50%, will take 10 amps for about 3.5 hours, before voltage reaches 14.5v at the battery terminals, then require 2-3 more hours above 14.0v to be in the 99.5% charged range. Lesser pressure = more time, and older batteries, lesser pressure will not be able to reach full charge no matter how much time one has.
Would you like to drive from A to B without an odometer, or speedometer on a featureless landscape, and have no good idea how to judge speed?
Knowing voltage /pressure a charger is delivering into the battery, is like saying my vehicle can go either 35mph, 75.27mph, or 100mph, but I have no idea where point A is, nor how far away B is, nor do know my speed, nor how far I have traveled. I'll just have the vehicle stop automatically when i see a green light and assume I am there.
Get an ammeter.
When amperage tapers to very low levels at voltages above 14.2ish, or stops tapering, the battery is truly fully charged. amperage the battery accepts at at float voltages ( less pressure) is much less informative.
If you dont know the amperage the battery is accepting, but only voltage, you have no idea whether you are travelling 35, 75, or 100mph, and with the Noco genius 1 anyway, you could simply be coasting towards 12.69v, after having gotten to 100mph, hours, or days, or weeks before.
Stop driving blind.
Splice these 12 awg leads inline on your charger( upto 25 amps). simple dimple, there is a source and load side. the charger will be the source, the battery the load.
https://www.amazon.com/GT-Power-Analyzer-Consumption-Performance/dp/B00C1BZSYO
it will show:
1. Voltage
2. amperage
3. wattage
4. Watt hours
5. amp hours.
6. Peak amperage
7. Peak wattage
8. Minimum voltage
9. some clones show Time, as well. some think 52 minutes is an hour, and the KWH figure is way off, but Ah are still accurate.
There are many dozens of clones of this wattmeter.
None are perfect, most are good enough.
Some do better than others reading accurately in the 0.3 amp range or less.
Some I've gotten, have been good down to 0.06amps, but at an actual 0.05amps it reads 0.00amps.
Others read 0.15a at an actual 0.3 amps and reads 0.00 at an actual 0.12 amps
I double check mine with other shunted ammeters, or a clamp on Ammeters.
Knowing how many amp hours the battery took before the charger shut off, is enlightening.
Knowing how many more amp hours the battery can accept after the smart charger shuts off, and an adjustable voltage power supply applied continues to hold the battery in the mid 14, is both frustrating, and enlightening.
On ~100 Ah batteries I found I could almost always stuff in 8 to 12 more amp hours via adjustable voltage power supply, after the smart charger said enough, green light for you.
Once I started regularly stuffing those additional 8 to 12 amp hours into the regularly deep cycling marine 12v battery, I started getting 'respectable' cycle life from them. Before that I was consistently disappointed with any brand battery, no matter how well I tried to recharge them with the tools I had, then.
How much difference it makes in a pure starter battery duty, is certainly up for debate.
Good enough, is subjective.
Opinion,
and there no shortages of uninformed versions of those, nowadays.
