Do I need a longer Absorption?

based on a post in this thread:

A 2 hour Absorption _can_ be enough;  depends on how much current the battery is still accepting at the 2 hour mark (subtracting any loads).   The important idea here is that the battery is accepting the current it wants;  the controller isn't forcing it into the battery.* The flow looks like this: > > > * Bulk charging continues until the Absorption voltage setpoint (Vabs) is reached. > > * then Absorption stage holds Vabs until either the time is up (2 hours in your case), or until the current into the battery drops sufficiently, or some automagic combination of the two. > > * then Float stage takes over and holds the Float voltage setpoint (Vfloat) > Sufficient current drop is usually described as falling to something like [C/200](http://rvwiki.mousetrap.net/doku.php?id=electrical:12v:battery_capacity):  (the bank's capacity in Ah divided by 200). So let's say your battery manufacturer specifies C/200.  In that case 400Ah/200 = 2A.  So when current accepted by the battery during Absorption drops to 2A, absorption is done.  I will use this pretend number from here on. Examples using C/200 and 400Ah: > > > * if the controller drops to Float when current is still falling toward 2A it is floating prematurely and the batts aren't getting tippy-topped off.  This is what you suspect your system is experiencing. > > * if the controller drops to Float fairly quickly after current stabilizes at 2A then it's on the money. > > * If the controller drops to Float a long time after current has stabilized at 2A then it is holding Vabs longer than it needs to.  In a flooded battery this could accellerate water loss and therefore require more maintenance.  I don't know the effects on AGM but probably minimal since AGM Vabs are already set lower than flooded..  My guess is it's better to run Absorption a too long rather than too short. > So your homework   is to turn off as many loads as you can at about 1.75hrs into Absorption and see how much current (in amps) is flowing into the battery.   If the battery is still accepting** > C/200.*** then the bank might benefit from a longer Absorption duration.  I don't think you mentioned what controller you have, but should you need to change that value hopefully another owner can chime in. more info if everyone hasn't already hung themselves: * If the controller tried to force in more than the battery wanted then the battery voltage (Vbatt) would rise.  But the controller is set to a particular Absorption voltage setpoint (Vabs) so it has to back off... - return ** for this reason sometimes Absorption is called Acceptance - return *** or whatever the manufacturer says.  Remember my number is fake. - return