Lifeline AGM batteries recommend charging rates of no less than 20% when deeply discharged
Page 19
http://lifelinebatteries.com/wp-content/uploads/2015/12/manual.pdf
Odyssey AGM recommedends a 40% charging rate when their battery is deeply cycled:
page 14:
http://www.odysseybattery.com/documents/US-ODY-TM-002_1214.pdf
As for AGMs not tolerating PSOC operation as well as their deep cycle flooded counterparts, I gleaned this info from a very experienced and highly respected marine electrician. If you want to argue physics vs experience in actual use, bring it up with him:
https://forums.sailboatowners.com/index.php?threads/agm-batteries-making-the-choice.124973/
My own experience with a Northstar AGM, Thin plate pure lead, similar to Odyssey, With many measuring tools and many many cycles watching a voltmeter, an ammeter and an amp hour counter, is that this particular TPPL AGM battery LOVES a high amp recharge from a well depleted state.
With a low and slow solar only( max 13 amps) recharge to full( determined by amperage at absorption voltage, after about 5 to 10 deep cycles, I notice voltage held during the next discharge starts sagging more and more each low and slow solar only recharge. Also my voltmeter during engine cranking drops lower and lower each first cold start of the day.
One high amp recharge( 40+ amps) from its most depleted state to truly full, and the performance is reset. This is not just becaise high amps heat the battery more and then that next discharge the battery is warmer and appears to have more capacity, as it performs well the next night too back at regular temperatures. Afer a high amp recharge to full, Voltage held under loads is impressive once again. It can accept more amps for longer before attaining absorption voltage, Amps at 14.7v taper to 0.5% of capacity in less time, and it cranks my engine with more gusto holding a higher voltage when doing so. This is repeatable, predictable and I am approaching 550 deep cycles on this battery over 36 months, and expect at least 800.
Stockrex, be careful with the universal 12v DC to DC power supply if your laptop can exceed 60 watts.
Multiply output DCamps times output DC voltage listed on the provided power brick, to get the maximum watts.
The Ciggy plug will likely melt at some point, well before the fuse blows. The Stink can be bad and stick around.
I use a 90 watt PWR+ DC to DC car adapter for my Dell. replaced the 12v plug twice before hardwiring it to fuse block and using 30 amp anderson powerpoles as the connector.
I would watch the volts at battery terminals with an actual voltmeter while the schumacher is charging on the AGM setting closely. My schumacher sc2500a will, about 20% of the time on AGM setting, exceed 15 volts on 12 or 25 amp setting, 2 amps on my current battery I chrge with it, cannot get voltage above 15 no matter how long it is applied.
On the other two settings, Standard or deep cycle, it will exceed 16 volts about 75% of the time. Ambient temperature plays no part in when it decides to get masochistic with the voltage.
The Display on my schumacher no longer works at all. i use a wattmeter on the DC output to see what it is doing and press one button 3 times for AGM, and the other button once for 2 amps twice for 12 amps and 3 times for 25 amps and verify output with the linked product below.
https://www.amazon.com/GT-Power-Analyzer-Consumption-Performance/dp/B00C1BZSYO
These wattmeters might, or might not be so great reading low currents.
I do not use the schumacher on any battery i care about, and I do use the AGM setting on a flooded battery as it will be less likely to shoot to 16+ volts, and it will float at 13.6v instead of 13.2v. It inevitably drops to float voltage too soon, so 13.6v float at least has a battery chance to get the battery near full charge before I unplug charger, unless I want to trick and restart the charger instead.
Keep in mind that recharging a regularly deeply cycled battery is different than top charging a lightly discharged battery here or there. Those using AGM's as starting batteries and never deeply discharging them need not freak out over not meeting the ideal recharge regimen. Those who do deeply cycle them and who do not recharge them fully properly and occasionally at a higher amperage rate, will likely not get their money's worth out of the battery.
The High$$ AGMS in deep cycle duty are only worth it if the effort is going to be made to rechagrge them according to their desires. The lower$$ AGMS can hurt less to replace more often and one can not shiv so much of a git when they become capacity compromised all too soon.
I'd aim for a charging source that can achieve no less than 20% of the capacity of the AGM battery, 20 amps per 100AH of capacity, and I would definitely use an Ammeter and learn how to force the charger to reseek absorption voltage. this requires loadig the battery with a larger load until voltage drops below 12.8v, then restart charger then remove load.
If one gets an Odyssey or Northstar AGM and deeply cycles them, I would aim for 40 amps per100Ah of capacity. Northstar documentation does not list any minimum charge rate, but Mine performs so much better when it get high amp recharged and I find it to be an impressive battery since i do charge it hard and fast and full, often. If I charge it slower to full daily, I notice voltage sagging more and more each cycle without the high amp recharge , and go out of my way to apply n less than 40 amps when it is most depleted, and try to do so before the sun rises and begins filling it slowly.
