cognitive dissonance said:
Special needs batteries. Who knew?
Do you recommend them for short buses?
I don't think any battery is going to out cycle a 6v flooded golf cart battery. These are simply the most tolerant of the type of usage typically seen in this lifestyle.
If one wants the AGM, and wants them to last, AND to cycle them deeply, then the high amp recharge needs to be done, every so often. The less deep the discharge, the less important it becomes to meet the high amp recharge on occasion.
But after many days of cycling deeply, and in incomplete recharge each day, then the battery capacity will have effectively shrunk to a smaller size, than the same size flooded battery treated the same way.
While the flooded battery at this point does not require any special current to return to near full capacity, given enough time at absorption voltage, the AGM battery wants, and craves, a higher initial recharge current to force the migration of electrolyte in the plates. If the high amp factor is not achieved, the battery will still appear to take a full charge, but if one were to have an AH counter, and notice voltage held for the AH removed, one would easily notice it is lower than expected, the battery is in effect starting out fully charged, but with less initial capacity.
I've seen this time and again with my own 90AH AGM. Even cycling to only ~66% state of charge and solar only recharging. After 5 cycles, the voltage held for the AH removed is 0.1 to 0.15v lower than on night one. This is even achieving 14.5v and amps tapering to 0.05% of capacity each day before ending absorption voltage and dropping to float.
Day 5 or 6 early morning, this battery, I drained to ~12.2v overnight, gets either 40+ amps from the alternator, and or my Meanwell 40 amp power supply, and the solar can then hold the voltage at 14.5 until amps taper to 0.4, and then it returns to full performance. It cranks my engine with a gusto it had lost in a solar only recharge regimen, and during discharge that night, the voltage held for the AH removed from the battery is back up in the impressive territory.
The Northstar is a high$$ AGM, like Odyssey and Lifeline. These batteries have no upper limit on charging amperage, as long as voltage is not allowed to exceed 14.4(LL)14.46(NS) and 14.7(Odyssey).
Lesser $$ AGM batteries exist. Like the Vmaxtanks on Amazon and the often rebranded Deka intimidator AGM sold at sams club and costco and elsewhere.
These lesser AGMS have a limit on charge amperage. no more than 30 amps per 100Ah of capacity. While exceeding this briefly is no big deal and hardly an instant battery killer it should be realized that these batteries, given a basically unlimited charging source, like a well wired cool vehicle alternator spinning fast, these batteries can drink faster than they should. These lesser $$ AGMs still appreciate the higher initial charge rates approaching this 30% rate. They 'might' also be more tolerant of a low and slow, solar only, recharge regimen.
They are certainly less painful to replace if they are killed prematurely.
Basically, the AGM battery, to live anywhere near the manufacturer's claimed cycle life, requires a more exacting recharge regimen, and the harder the battery is used( depleted deeper) the much more important proper recharging becomes. The 6v GC battery is simply more tolerant of less than ideal recharging. It is the easiest battery to keep happy. and costs the least if one needs 220AH of house battery capacity. Dealing with the offgassing, occassional watering, and their increased height, is the only downside with them.
But one can get 220Ah of GC battery for 200$. 220 AH of AGM is looking at 375 to 650$ just for the batteries, and a solar controller with programmable settings is more$$. Wiring up the alternator becomes more necessary, more time and $$, and a plug in charging source likely should be factored into the equation too. One which can approach a 30% rate, or ~ 65 amps for 220AH of AGM battery and whose absorption voltage is close to that recommended by the AGM manufacturer.
So no only do the AGMS cost more, the charging accoutrements required to meet their peculiar desires cost more too.
While AGMs are considered a no maintenance battery, if they were a person one is in a relation ship with, they would be considered high maintenance., and only with a surplus of everything they want, could they be kept happy.
http://www.allbatterysalesandservice.com/browse.cfm/4,576.html
If I ever buy another deep cycle flooded battery again, I am getting this one:
http://www.trojanbattery.com/product/t-1275/
I could stuff it underhood where the original battery mounted, with some modification.
My Van cannot tolerate the height of 6v GC batteries, without sacrificing ground clearance and much other modification. I am not willing to lose interior space or share the air with them either.
If it/I could, No way would I be cycling this 325$ Stubborn princess AGM.
My plan is to make this AGM last until I have a Solid grasp of LiFepo4 and the funds to set them up properly, and more trust in the purveyors of these prismatic cells.