X2Power Premium AGM BCI Group 27F Car and Truck Battery G-27F not holding charge

Oct 16, 2010
Equating voltage with a state of charge or state of health, is unwise, as there are so many factors which will fudge the numbers and lead to false interpretation, and incorrect assumptions.

Voltage is only accurate as to state of charge, when there is/are NO loads on the battery, for many hours, and it has had sufficient time after charging, for the surface charge to wear off. This surface charge depletion, can take days on a healthy battery, and just blasting the lights on for a few seconds or minutes to deplete the surface charge is also not going to definitively prove anything.

When checking voltage in the vehicle, hood open, does anyone know how much load is actually on the battery, or was on the battery when they opened the doors, and is still on the battery when they finally put the leads on the battery terminals?

My group 31 Northstar will stay at 13.06v, but when I turn the key to on and lower the windows, which is about 7 amps per window, voltage falls to 12.78v, and if I turn key off, removing all but a tiny parasitic load, voltage will rise back above 13, but it will take an hour to do so, when at 70F, and at 55f take many hours.

Voltage is completely unreliable, and equating a voltage with a state of charge can only be somewhat accurate when all the variables are accounted for, repeatable, and compared with earlier data, on the same battery.

This 12.xxv = xx.x% is asinine in the extreme.

While AGMS have been marketed as superior batteries in each and every way, the sad fact is that they will degrade faster when they do not get returned to true full charge regularly, especially in deep cycle service.

In deep cycle service, they will be ticked to a premature demise with the 'trickle charge it overnight' mantra so often repeated here and elsewhere.

Odyssey states than in deep cycle service their batteries should receive no less than 40 amps per 100 amp hours of capacity. When still healthy, they can accept far more than 40 amps. My group 31 Northstar AGM had No issues what so ever accepting 134 amps, when drained to 50% state of charge or below.

People also like to falsely state that too low a voltage will not truly fully charge a battery. Completely utterly false no matter how often it is repeated.

This is like saying that you will only get to your destination if you drive 80mph, if you drive 70mph, you'll never get there.

Lower charging voltages just take longer to get the battery to higher states of charge.

Smart chargers, can truly fully charge batteries, especially healthy ones, one just needs to know when that light goes from red to green, and charge voltage falls from mid 14's to mid 13's, that at that point the battery is NOT fully charged. It can take 12+ more hours at 13.6v to reach 100%. going from red to green only means has dropped from absorption stage, to float, and charged enough to start the vehicle.

Older batteries might need 24 hours held at 13.6v to get from 96% to 100%
batteries close to end of life will likely never get to 100% held at 13.6v forever. They likely will just start heating up and require more and more amperage to be held at 13.6v. The beginnings of thermal runaway.

I'm on my Second Northstar. the first group 27 was easily the bast battery I've ever cycled to death. 1200 deep cycles and many thousands of engine starts over 6 years. The key to this longevity was hitting it with no less than 25 amps initially, whenever it was drained near 50%, but also holding 14.4 to 14.8v until amps tapered to 0.4 or less. This was when new, no less than a 6.5 hour process, and when older no less that 10, and the last 200 cycles amps never tapered to 0.4, but would bounce off some level just above this, and then start rising as battery temperature started increasing.

My Second northstar, a group 31 is being treated better, but is not as impressive. Did their quality take a downturn in ~ 2018? seems possible. Could it just be the lead/electrolyte ratio, also possible

The thing with these TPPL Agms, is they get lazy when never cycled deeper. Mine, when just held at high states of charge, would/will get lazy. They do not hold as high a voltage powering lesser loads for 12 hours, nr when supplying the 230 amp burst needed to get motor turning or the 180 amps to keep it turning till it caught.
Every time I noted this lazyness, I would intentionally drain the battery to less than 50% state of charge, in 6 to 8 hours, and then allow it to feed on less than my 40 amp adjustable voltage power supply set to 14.7v. I have a 100 amp power supply too( really 97.7 amps) , and I can put them in parallel.

At first, taking the ~35% charged battery would quickly rise to 14.5v, requiring about 75 amps, but over the course of a minute the voltage would fall to 13.8 and the amps would rise to ~134, and then the voltage would begin its rise back up to 14.5. Once voltage reaches 14.5v then the amperage required to hold the battery at 14.5v begin to taper. Once they taper to 0.5 per 100AH of capacity then the battery can be considered fully charged, or nearly so, but dropping voltage at that point to 13.6v and holding it for 6+ hours, if one then raises the pressure back to 14.5v amps will taper to 0.0x.

These high amperage blasts from a well depleted state are the smack across the face of a lazy thoroughbred AGM Lead acid battery. The high amperage forces migration of the electrolyte deeper into the sulfate occluded plates, and warms them, helping to dissolve the sulfation.

If these thoroughbreds are only ever asked to start a modern fuel injected engine, they will get bored and lazy and perform no better than the cheapest battery one can find. Their voltage retention under load will become less and less impressive. Their ability to accept huge charging amperages and charge from 50% to ~85% quickly will decline. that last 15% always takes hours, but the less healthy the battery the longer it takes, even if held at 14.7v.

Modern vehicles whose voltage regulation is programmed for max MPGS, will further degrade the TPPL AGMS more quickly, as for this strategy to work, the battery needs to be around 80% charged, as at 80% it can still accept 25+ amps when the voltage regulator suddenly demands 14.8v. If it were at 99% charged the battery would only take 4 amps for a second before voltage rose to 14.7v.

All lead acid batteries ideally want to be kept truly fully charged and kept cool.

Regular consumer grade AGMS, and TPPL high $$ AGMS, if deeply cycled, should be fed higher amperage from their most depleted state.
Most consumer grade AGMs, like the bitog favorite rebranded Deka intimidator, say to limit amperage to 33 amps per 100Ah of capacity, and Odyssey TPPL AGM$, says no less than 40.

a 33% charge rate or a 40%.

I've fed My Northstars 134%, my Dekas intimidators 57%, I just watch their temperature.
I dont do this every recharge, only when they have gotten lazy from not having to work, or when cycled deeper but never returned to 100%.

Paying top dollar for a TPPL AGM, only makes financial sense when they battery is going to be intentionally discharged deeper, and can then feed on a high amperage potential charging source to return to 85% charged quickly. In such service they will need to be returned to a true 100% state of charge( meaining being plugged in to a charging source capable of holding them at higher absorption voltages until amperage tapers to low levels) to have any hope of retaining that impressive( when new and healthy) performance. They will lose this potential performance quickly if never worked hard and charged at a high rate from their most depleted state. If they never get drained below 80%, and high amp recharged to truly full, they will never be able to accept high enough amperage for long enough, for them to retain their once impressive abilities.

And those hoping their recently polished 200 amp alternator can feed them properly, well he potential is there, but not when the vehicles voltage3 regulation does not allow it. Also, 50% to 100% charged is never less than a 6.5 hour process, even with 100+ amps available and the battery brought to and held at 14.7v the whole time.

AGMs really need to stop being perceived as a better battery. They are not immune to improper care and feeding, if anything they are the petulant princess of the battery world demanding and fickle when asked to work hard, and demanding and fickle when sheathed in diamonds, and fed bon bons too.

if bought as a bragging rights battery, well feel free to brag for ~ 6 months, and bragging after that point is unwise in the extreme unless one can work them hard and also feed them properly.

no vehicle will feed them properly, there's just variations of less than ideal.
Ideal takes special equipment, and time, and the desire to monitor pressure and flow during.

ODYSSEY® Battery Reconditioning Charge Procedure

Jan 31, 2006
....If these thoroughbreds are only ever asked to start a modern fuel injected engine, they will get bored and lazy and perform no better than the cheapest battery one can find. Their voltage retention under load will become less and less impressive.....
I've observed this with my 2 year old X2Power/Northstar battery in my Subaru. In addition to the lower voltage under load there is also a lower voltage after charging. When new the battery would be at 13.00V (OCV) at 30F, 48 hours after charging with a 20A smart charger. These days it is down to 12.75V at 30F. But I don't regret buying this $230 battery in January 2001. It comes with a 5 year full replacement warranty. I expect to get a free battery in 2024 or 2025.