Group 27 AGM mid life performance report
My 90AH Northstar AGM battery is now 38 months old, and has accumulated ~465 deep cycles.
When I cycle it, generally I consume 35 to 65AH nightly, average about low 40's
Since June of 2015 it has been my Only battery, for house loads and engine starting as I saw it had absolutely NO issues cranking my engine to life quickly when depleted 68 of its 90AH.
However, I have been noticing its age. The previous deep cycle it only required some 45 amps to reach absorption voltage, and it then took forever for amps to taper to 0.5% of capacity at absorption voltage. This was noted after many nights floating and very light cycles end of afternoon, previous to the deep cycle.
Despite this, the voltage held during my normal overnight loads had not decreased in comprison to when new, unless I went 5 partial state of charge deep cycles, or did not have ANY high amperage charging during that 5 day period.
So Last night I did a test. I drained it to ~60Ah from full in about 6.5 hours, and then applied 65 Amps fo charge current.
Anyway at ~60Ah from full, perhaps 33% charged, I turned on my inverter and powered a 200 watt electric heater for a minute for a total load of 22.x amps.
Voltage dropped to 11.5 under that 22 amp load at that level of battery depletion.
2 minutes after removing the inverter load, at 5.6 amps of load, voltage rebounded to 11.7v
2 minutes after that, under a 1.7 amp load voltage rebounded to 11.9v.
2 minutes after that under a 0.3 amp load, voltage rebounded to 12.02v, and then I applied my charging sources.
Schumacher's 25 amps were first
Meanwell's 40 amps were second.
Battery temperature was 63F, and the goal was holding 65 amps until ~14.8v was attained at battery terminals.
Voltage quickly rose to 14.4v, but then levelled off, then dropped to 13.9v over the next 5 minutes, then started climbing again at a constant 65 amps of charge current.
24 minutes later the schumacher started dropping amperage as battery voltage approached 14.7v, and then voltage sagged to 14.5v. I guess the schumacher was not in its masochistic mode where it seeks 16.4v at maximum amperage output.
6 minutes later the battery hit 14.8v under 53 amps of charging source. 40 from meanwell, 13 from Schumacher.
40 minutes after applying 65 amps initially, Amps had tapered to below 40, and I removed the schumacher with meanwell providing the 35.5 amps required to maintain absorption voltage.
Battery temperature had risen from 63F to 77F in those 40 minutes and I decided to start reducing absorption voltage to maintain 14.6v.
This required some babysitting, as there is some voltage drop on my 8awg cabling from meanwell to batteryswtch and battery switche's 2awg to battery. The battery was still warming pretty rapidly despite the dropping amperage.
Amps had declined to 4.6 at 14.6v at the 2 hour mark and battery was well over 80F in sub 60F ambient temps and still warming.
I did not stay up/awake for the time required for amps to taper to 0.45 @14.6v, nor did I want to leave it at 14.6v while I slept, So I lowered voltage to 13.9v and went to bed.
~3 hours later or so battery was accepting 0.1 amps at 13.9v and I goosed voltage to 14.7v again. It took 1.7 amps initially, and then dropped to 0.4a in the time it took to empty my bladder. So it was basically fully charged 7.5 hours after initiating 65 amps with ~ 3 hours at the end with 13.9volts, rather than 14.6.
I lowered voltage back to 13.9v and slept for 3.5 more hours
Awoke to 0.1 amps at 13.9v and a voltage goosing to 14.7v again took 1 amp but that quickly tapered back to 0.1amp.
It used to taper to 0.0x? amps at any voltage when a charging source was applied this long. now it will taper to 0.0x amps, but takes about 15 to 20 hours to taper to that low an amperage.
So the battery is still performing very well, in my opinion. Aging gracefully despite working hard, and still packing a punch.
It should be noted that all my charging sources, Solar, Alternator, and Meanwell power supply, are adjustable voltage, except the schumacher, which I use on this AGM seldomly, only when 40 amps is less desirable than 65, for whatever reason. 2 of these 3 sources were either not present or adjustable 38 months ago.
When I cycle it, generally I consume 35 to 65AH nightly, average about low 40's
Since June of 2015 it has been my Only battery, for house loads and engine starting as I saw it had absolutely NO issues cranking my engine to life quickly when depleted 68 of its 90AH.
However, I have been noticing its age. The previous deep cycle it only required some 45 amps to reach absorption voltage, and it then took forever for amps to taper to 0.5% of capacity at absorption voltage. This was noted after many nights floating and very light cycles end of afternoon, previous to the deep cycle.
Despite this, the voltage held during my normal overnight loads had not decreased in comprison to when new, unless I went 5 partial state of charge deep cycles, or did not have ANY high amperage charging during that 5 day period.
So Last night I did a test. I drained it to ~60Ah from full in about 6.5 hours, and then applied 65 Amps fo charge current.
Anyway at ~60Ah from full, perhaps 33% charged, I turned on my inverter and powered a 200 watt electric heater for a minute for a total load of 22.x amps.
Voltage dropped to 11.5 under that 22 amp load at that level of battery depletion.
2 minutes after removing the inverter load, at 5.6 amps of load, voltage rebounded to 11.7v
2 minutes after that, under a 1.7 amp load voltage rebounded to 11.9v.
2 minutes after that under a 0.3 amp load, voltage rebounded to 12.02v, and then I applied my charging sources.
Schumacher's 25 amps were first
Meanwell's 40 amps were second.
Battery temperature was 63F, and the goal was holding 65 amps until ~14.8v was attained at battery terminals.
Voltage quickly rose to 14.4v, but then levelled off, then dropped to 13.9v over the next 5 minutes, then started climbing again at a constant 65 amps of charge current.
24 minutes later the schumacher started dropping amperage as battery voltage approached 14.7v, and then voltage sagged to 14.5v. I guess the schumacher was not in its masochistic mode where it seeks 16.4v at maximum amperage output.
6 minutes later the battery hit 14.8v under 53 amps of charging source. 40 from meanwell, 13 from Schumacher.
40 minutes after applying 65 amps initially, Amps had tapered to below 40, and I removed the schumacher with meanwell providing the 35.5 amps required to maintain absorption voltage.
Battery temperature had risen from 63F to 77F in those 40 minutes and I decided to start reducing absorption voltage to maintain 14.6v.
This required some babysitting, as there is some voltage drop on my 8awg cabling from meanwell to batteryswtch and battery switche's 2awg to battery. The battery was still warming pretty rapidly despite the dropping amperage.
Amps had declined to 4.6 at 14.6v at the 2 hour mark and battery was well over 80F in sub 60F ambient temps and still warming.
I did not stay up/awake for the time required for amps to taper to 0.45 @14.6v, nor did I want to leave it at 14.6v while I slept, So I lowered voltage to 13.9v and went to bed.
~3 hours later or so battery was accepting 0.1 amps at 13.9v and I goosed voltage to 14.7v again. It took 1.7 amps initially, and then dropped to 0.4a in the time it took to empty my bladder. So it was basically fully charged 7.5 hours after initiating 65 amps with ~ 3 hours at the end with 13.9volts, rather than 14.6.
I lowered voltage back to 13.9v and slept for 3.5 more hours
Awoke to 0.1 amps at 13.9v and a voltage goosing to 14.7v again took 1 amp but that quickly tapered back to 0.1amp.
It used to taper to 0.0x? amps at any voltage when a charging source was applied this long. now it will taper to 0.0x amps, but takes about 15 to 20 hours to taper to that low an amperage.
So the battery is still performing very well, in my opinion. Aging gracefully despite working hard, and still packing a punch.
It should be noted that all my charging sources, Solar, Alternator, and Meanwell power supply, are adjustable voltage, except the schumacher, which I use on this AGM seldomly, only when 40 amps is less desirable than 65, for whatever reason. 2 of these 3 sources were either not present or adjustable 38 months ago.
