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4 year old Northstar AGM stress test
I bought this battery in November of 2013. 

It is a group 27 battery rated at 90AH capacity, and 930 cold cranking amps.  It weighs 67Lbs.

Note that typical marine flooded group 27s are rated at as much as 115Ah capacity and about 650CCA, and weigh about 55Lbs.

Trojan claims their group 27 has 105AH and is 55Lbs and their other 27 has 115Ah and weighs 61 Lbs.

What does a wally world flooded group 27 weigh?   10 years ago my WW marine flooded -27's weighed 51.5lbs

My Northstar initially  saw fairly light usage, mostly as a starting battery with perhaps one deep cycle each month, Until june of 2015 when it got put into double duty as house battery and engine starting battery.

Since then it has been my only battery.

Since then the battery has accumulated  about 700  total Deep cycles on it.
I will guestimate about 50 Cycles  to well below 50% some as as low as 20% State OF Charge.  It never had any issue starting my 318 v8 engine in mild temperatures when drained this low.  It did not even seem to crank much slower, which was a bit of a mind boggler.
~250 cycles  to 50% SOC
~350 to about 62%
about 50 to about 75%.
probably about 500 cycles to 95% and several thousand engine starts, but these cannot be considered deep cycles.

I really tried to get it back to 100% charged after almost every cycle, by alternator, 198 watts of solar and plug in charging sources.  I never went more than 5 days without getting it back to 100% true full charge.

The more days that it went without a full charge, the longer the absorption stage took.
The more days it went in a row with just low and slow solar as the only charging source, the longer the absorption stage took and the more important it seemed to be to hit it with higher amps when most depleted.

While worked hard,  this battery has also been treated pretty good in that I tried to get it back to full charge often.

In Sept 2014 I got the 40 amp meanwell adjustable voltage power supply(RSP-500-15), so that i could hold absorption voltage as long as needed.  In January 2016 I modified my vehicle to allow me to use an external voltage regulator controlling the alternator, so I could choose the electrical pressure, so there was some time when I could not achieve Ideal with this battery.  The solar settings could be adjusted, and On the advice of Mainesail, I bumped up voltage to absorption voltage 14.7 where Northstar recommends 14.46v at 77f

But now This battery is obviously loosing CCA, and capacity, and is taking a long time to fully recharge, and if i could not plug in to the grid, to  achieve the full recharge, it would have been recycled and replaced by now.

Today, it was fully charged when I drove to the gas station.  I was playing some Music at some good volume.  My 45 watt heating pad was under my showerbag  My fridge compressor could have been running.  Anyway after 20$ worth of gas I started the engine, and the stereo kicked off during  engine cranking.  This is a sign it was not able to maintain a high enough voltage to keep powering the stereo, and the first time in a long time that it has occurred, the last time being when it was well depleted  below 50% SOC, starting an overnight cold engine.

But the battery has been living pretty easily lately, not getting any high amp recharges and not getting discharged much overnight, I've been pluggin in, as I do not know when I could afford replace it with another Northstar battery, So i have been saving its remaining cycle life.

I am impressed enough with the battery performance to this point, I definitely would buy another one.
But I am also not willing to give up on it entirely.

The battery has always responded well to a high amp recharge from a well depleted state.

From about 4PM to 11PM, I removed 45AH from it.  Then I powered my 200 watt heater from my inverter, and the load on the battery went as high as 30 amps with fridge laptop and other loads, and I took it down to 11.3 volts at that 30 amp load. 

These huge loads diminish available battery capacity, so while my battery monitor said 56 AH from full, the battery would have 90AH if new fully charged, and discharged at 4.5 amps.   Since the average rate of dischrge was well over 4.5 amps there was No way the battery had 90Ah of capacity to give, yet it still did surprisingly well

At 11:56 I removed all loads but 0.4 amps .  Voltage rebounded to 11.8v
At 12:00 voltage was 11.89 volts and I applied 65.5 amps of chargers, a 25 amp schumacher and a 40 amp adjustable voltage power Supply set to 15V.

After 24 minutes of the battery accepting 65 amps, the voltage has just hit 14.7v.  The battery has risen from 61F to 72.7F
 My battery monitor says the battery is now 34Ah from full, But I am not really putting much faith in that reading.

HOw much longer will it take for the battery amperage, at 14.7volts, to taper to 0.45amps, at which point the battery can be considered fully charged.

I do not know if I will be awake when that occurs.  If the battery were still new it likely would likely occur about 6:30AM.
I will guess it will be around 9:30, but I guess it could be later.

Once amps taper to about 35, I will turn my fridge back on, and remove the schumacher charger, 

Now at 12:28:45 it is holding at 14.7, accepting 56 amps. battery is upto 74.5F.  The temp sensor is on the battery casing, the plates are no doubt  hotter.

Will the battery behave any better.  will some of those lost CCA and capacity be returned?
Some will. I do not know how much.
but I do know that few batteries could handle this charge rate and seem to love it.
12:32:00---  14.7v 50.9 amps 76.5F

Once it gets to 77F I will think about lowering the voltage slightly.

The ambient temperature  by battery is about 56F

12:44:20 14.6v  32.3 Amps "21Ah" from full  battery temp 81.1F.  21 is in quotes as i do not trust my battery monitor when obviously so much of the amperage is being turned into heat by the resistance of the battery.

I just removed schumacher.  The wattmeter said it returned 21.546AH
The wattmeter on the meanwell reads 29.82AH

so the wattmeters are claiming I returned 51.336 AH
My battery monitor is saying I returned  37Ah

I wont know it is truly full until amps taper to 0.45 or less.

Now that my fridge and other loads are back on, the wattmeter AH figure will be invalid as some portion of the output of the meanwell power supply will be powering this laptop and my fridge, and Keeping my showerbag at 100F

12:53:25 14.6v  22.9amps   '17' ah from full 84.4F

1:00:30  1 hour into recharge. 14.6v  battery is accepting 18.7 amps  '16' AH from full 84.6f

1:19:xx  14.6v  11.4 amps  "11AH" from full  87.3F

While the battery seems to have recharged pretty quickly to this point, it could take 8 more hours for amps to taper to 0.5% of capacity, or 0.45 amps

The problems with lead acid batteries, is if they do not get the time required to achieve the 100% full recharge, they run screaming towards the edge of the cliff and do a belly flop.

As they age this time to full takes longer and longer.

I'll try and awake at a reasonable time and check amperage and will update, but I am going to leave it at 14.59ish volts until then.

1:27:xx 14.59v  9.2 amps  88.3F

Battery temp is still rising pretty fast.  Gonna lower voltage more

1:28:xx 14.41v 8.8 amps  88.3f

Readers should note that it took 24 minutes for this very depleted battery, for its voltage to rise to absorption voltage(14.7v), at a 65.5 amp charge rate.  The ONLY way to speed the overall charging, would be to allow a higher absorption voltage( not recommended or wise) which would allow those 65.5 amps to flow for longer, OR,  to increase the initial amperage, and then 14.7v would be reached slightly earlier.  Perhaps 80 amps would achieve absorption voltage in 17.5 minutes instead of 24.  Since the full recharge of the well depleted battery cannot be achieved in less than 6.5 hours......

Once Absorption voltage is reached, the battery is being recharged as fast as it safely can be recharged.  The battery itself dictates how many amps it can accept at the electrical pressure (voltage) applied to it.

This battery can handle a huge charge rate, 65 amps in a 90AH battery
Odyssey AGM batteries say no less than 40 amps in a 100Ah battery, when cycled to 50%
Lifeline AGM says no less than 20 amps per 100Ah capacity, and more is better
Trojan recommends a 10-13 amps rechrge their 100AH flooded battery.

How much time do you have?

1:41:25  14.46v  6.3 amps  89.4f
[-] The following 6 users say Thank You to sternwake for this post:
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Much to my surprise, at 6:30 am the battery was accepting only 0.2 amps at 14.41v, which was three hours earlier than my estimation to reach full charge. Forgot to look at its temperature.

I hypothesize that the extra ~20 amps of load, being the 200 watt heater on the inverter, applied when the battery was already 45Ah from full, had something to do with it. I really was expecting the low voltage alarm on my inverter to kick on before midnight occurred, but I wanted to start the recharge at that time and ended the discharge.

Odyssey AGM batteries are very similar to Northstar batteries.

Their reconditioning procedure says to drain battery to 10.0v with a high load then recharge at a very high rate.
Quote:Discharge the battery using the vehicle head lights or connecting some electrical
load to the battery and discharge to 10.0V under load measured with a hand-held
digital volt meter. Once 10.0V is achieved, disconnect the electrical load or turn
off the headlights or other electrical system or device.
2. Begin recharging with an approved charger as listed at
and with appropriate amperage for the capacity of the battery, minimum 40%
amperage of the 10 hour capacity rating of the battery. Utilizing chargers that
achieve 14.7V during charge and 13.6V in float are ideal. Monitor the batteries
terminal voltage with the charger operating to assure 15.0V is not exceeded at
any time. Charge the battery until the charging amperage seems to be near zero
amps and if the charger has a 13.6V float, float charge for 8-10 hours.

Please note that a vehicle headlights, without fog lights, are generally a 15 to 18 amp load, so it might take hours to get a battery to 10.0v. An inverter powering a big load is helpful for this intentional quick discharge, but do not go too big. 30 amps for a 90Ah capacity battery is about as much as I would go and perhaps stop at 10.5v instead of 10.0v, the low voltage alarm/cut out on the inverter might take care of that anyway, but it is impoortant to not let the battery sit in this extremely depleted state, but nearly immediately get the high amp charging source applied.

I did not take my Northstar to 10.0v, lowest it read with 30 amps of load right before I turned on the chargers, was 11.3v

I've not started the engine and cannot judge if there is an improvement in CCA, nor discharged it to see if voltage held for AH removed is higher than last night.

It always has improved after a high amp recharge before, this one was a bit different with the 200 watt heater applied when it was already below 50%, and I used the 'regular' setting on my Schumacher, and it held its voltage a bit higher. Most other times i did not bother turning off the fridge and all other loads so the charging amps varied between 59 and 63.5, instead of a constant 65.5 amps like last night.

Please note that many lesser $$ AGMS will not handle this rather extreme charge rate. They will likely heat up much more than the Northstar Did, and offgass more.

While it is said AGMS do not offgass, they do, but only about 2% that of a flooded battery, and only when recharged fast and hard.

There is a chance that this battery is getting low on electrolyte. Before I modified my vehicles voltage regulator, it would choose either 13.7 or 14.9v 95% of the time. Even with a full battery, for whatever batcrap crazy reason, going down the road, it would randomly choose 14.9v for a period of time. The battery location under the body behind driver exposes it to engine heat when moving.

The flooded battery that I bought at the same time as this AGM, a group 31 USbattery, and which was removed from service at about 500 deep cycles in June of 2015, recently had its plates exposed as it mostly sees the wacky schumacher, which will take it to 16.4v whenever it first receives 120Vac.
It was holding much higher voltages than expected long off the charger, days and still be 13.1+v, and now after watering and an extended EQ charge, the electrolyte will not raise above 1.260 and voltage within 3 days off the charger falls to 12.58v with just a 0.03 amp load.

It is the voltage and amperage and how they vary when charging and discharging, which can give one clues to battery condition/performance, but the hydrometer is the polygraph.

Nobody needs to go this far, I am hoping that this info simply helps people to put some puzzle pieces together, and perhaps they can, with some effort, greatly extend the time between battery replacement cycles.

It really helps to treat a battery right from cycle number one, as it is hard to reverse sulfation, and the process by which it is done, is abusive itself.
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  • Snikwahjm (01-03-2018)
Since sundown, I pulled 54Ah from the battery. The battery monitor was reset a few days ago and that 54Ah from fullshould be fairly accurate.

But I pulled that much out at a mucch higher average rate wat which the battery was rated at 90AH. My ammeter for the last 2.5 hours never dropped below 10 amps and went as high as 14.4 amps.

At 10:42PM It was:

54AH from full
13..3amp load
67.5f ambient temps.

Then I removed all but 0.2 amps of load and waited 4 minutes
Voltage rebounded to 12.00v in a minute and then 3 minutes later was 12.06v and was not rising quickly.

I then quickly applied 65 amps of chargers to this 90AH( when new) Northstar AGM.

I started the 25 amp schumacher first on the 25 amp setting and 'regular' meaning flooded starting battery.

I had My Meanwell rsp-500-15 unloaded and turned upto 15volts., and then plugged the8 awg leads with 45 amp anderson powerpoles together and instantly 40 more amps were feeding the battery.

Battery voltage rose to 14.4 quickly, but then, then over the next 3 minutes, it dropped to 14.1v as it was gobbling up 65 amps.

19 minutes later, it reached 14.7v, and amps began to taper from 65.

Battery temperature rose to 70.9, a gain of 7.4f

7 minutes later still at 14.7v in this constant voltage, absorption stage.
Accepting 53.8 amps. Battery at 73.6f

5 minutes later, 45.9 amps, 75.9f
1 minute later Shumacher providing 13.23a, MW 32.41a

11 minutes later 31 amps, 80.1f battery
3 minutes later 27.3 amps 79.7f battery. Now falling.
Ambient temp of ground under van, where battery is just above, is 63.5f

1 hour after first applying 65 amps, amps have tapered to 17.9 and battery is 73.9f.

Interesting that Schumacher is providing 13.3 of those while the meanwell is providing 8.66. ( I turned on many of the DC loads again) The meanwell was st for 15v, unloaded so the schumacher must be seeking a bit higher a voltage. the 0.25 voltage drop is more than I like, but not significant, since i can just twist the dial higher to compensate for it.

These high amp recharges always seem to make this battery perform better for many nightly deep cycles afterwards, holding higher voltage for the same AH removed. I had not noticed any significant deterioration lately, In fact with the longer days and higher sun, and now with daylight savings time the battery was seeming to perform very well during overnight discharge.
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Great report !
Real world testing and results is so much better for those learning vs. say IF someone was just copy pasting a website spec sheet. Wink Tongue
Stay Tuned

Weirdo Overlord  YARC
13 "Stinkin'Badges"  a "Full Monty Badge" 2 "Just Ignore Me" clusters  4 "Pine Cone" clusters  one "Stinkin' Badger" and 5 of the coveted "Flying Manure Spreader"awards!
1 of which is a limited edition Turkey Poop Spreader (What a "Stinkin' " honor !) + ROOIRIA

I awoke late, to a weight on my chest and furry paw tapping the middle of my forehead, so i do not know what time amps tapered to 0.4, but at 10am it was accepting 0.2 amps at 14.7v.

My last recording at 1:19AM ( charging started at 10:53pm) was 1.9 amps

It is interesting to have expectations of performance and then testing, and seeing if those expectations were met, and if not, trying to figure out why.

This battery is obviously aged, but in the voltage held for AH removed, the regular overnight discharge, it still performs admirably. The signs it is not what it once was is during engine starting. Voltage drops farther and far enough for my stereo to kick off if the volume is more than 1/5 of max.

The time for amps to taper to 0.4 at 14.7v has increased too, but sometimes is much more pronounced than others. This time is extended when the battery has not gotten fully charged enough cycle after cycle, which I try and avoid, but there is also something else at play that I have not yet put my finger on.

I love how this battery can accept huge recharge rates, and recharge quickly to the 90%+ range. Since I can control the voltage the alternator is told to seek, with an Hour drive I can basically get the battery to 90% from 30%.

Idling would be different story as hot at idle my alternator is good only for 50 amps, and 8.2 of those are feeding the fuel pump and ignition, but a few more hundred rpms can be up in the 75 amp range, and at 1950rpm, which is basically 65mph highway cruising can hold 85 to 90 amps of output, and be in no danger of overheating.

Idling maxed out has the alternator temperature skyrocket, in addition to not being able to feed the battery more than the 41.8 amps. Since it accepted 65 amps for 19 minutes this time, before reaching absorption voltage, Idling to recharge at 41.8 amps would not only have the alternator up in the danger zone in the temperature department, it would not be charging the battery as fast as it could be charged.

With the Renogy gift certificate, I was considering one of their chinese AGM batteries, but these all say to limit charging amps to no more than 30% of capacity, perhaps less. My Northstar AGM is accepting double that rate from my plug in charging sources, and my alternator at rpm could triple it, and this battery seems all the happier for it, when it gets it, and the thing has been in service since November 2013 and has ~ 750 deep cycles, with likely a hundred of those to the 35 to 40% charged range and a dozen or two even lower.

If it fails tomorrow, I'd have no issues, other than finances, in acquiring another one of these Northstar batteries.

Also, when this battery was new, i could not really properly charge it, I could not adjust voltage, I did not have more than 25 amps of plug in charging sources, i could not control my alternator, the only thing I could control was my solar setpoints, and no way could solar alone keep this battery happy.

So if I could have treated this battery better when new, it would perform even better today, than it does.

And thats part of why I go a bit overboard on the recommendations to seek and hold of proper absortion voltages for long enough, as when it is done regularly, the lead acid battery can perform very well. Even mild chronic undercharging of them will severly impact their cycle life, more than the mild chronic overcharging of them will.

And I have, like last night, held absorption voltage for significantly longer than required, many dozens of times. The battery is not dried out, or melted, or ever even come close to thermal runaway. If the slight overcharging of it has caused positive plate degradation, and has reduced the lifespan, all I can say is that it is 51+ months old, ~750 deep cycles, and is still performing admirably.
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