4x4van wrote:
Interesting. So you're saying that even though the amperage tapers down on the charger, the voltage stays high, and could push the actual battery voltage way above safe levels if left on too long? I have in fact left my charger hooked up overnight AFTER the meter has tapered down to zero and the green "battery charged" LED comes on, but I've never actually checked the voltage that the charger is putting out, neither when first hooked up nor after it has tapered down; guess that's something to put on my "to do" list next time I need to use the charger.:C
Usually thegreen light means the charger has stopped applying 14.x volts. It might either completely shut off, or hold a 'float' voltage which on a flooded battery is around 13.2v at 77f and 13.6v on an AGM at 77f with a few variances depending on manufacturer.
The ammeters on chese chargers are not to be trusted without confirming it, and like most 'smart' chargers will actually stop absorption voltage before the battery is indeed full.
Charging does still occur at float voltage, but at a very tiny rate as the electrical pressure is so low.
So voltage tells only part of the story, how much amperage is flowing at that voltage tells nearly all of it. Unfortunately, I have found on the three different chargers that have their own needle analog type of ammeters, to be generally representative of current high vs low but nowhere near the actual numbers printed along the bottom when tested with a known to be accurate DC clampmeter or an inline shunted wattmeter and often, both.
Good enough for most starter battery/garage applications, and any charging is better than no charging, but the regularly cycled lead acid battery craves the true full charge applied regularly, and plugging in for many hours with a charging source incapable of achieving the true full charge, just ain't right.
The key to reaching true full charge is holding the battery at high enough voltage for long enough, and no longer. Few automatic chargers do a good job at even approaching this ideal.
The inability of chargers to hold high enough voltage for long enough to truly fully charge a hard working deeply cycling battery, has had some of us resort to adjustable voltage power supplies that seek and hold a chosen voltage until turned off, by a human or a timer set by a human.
I have achieved a nearly unbelievable amount of deep cycles from my current AGM battery by insuring I can get it truly full, often, and I take it well below 50% state of charge, often.
