First Post - ROLLS AGM S6-275

Note that a Lead Acid Battery is "full" when resting at 12.7 volts... Above that voltage, the battery is "charging". Below that voltage, it is "discharging".

Especially with AGMs, they have higher resting voltages when first disconnected from a battery charger (13.0 volts or higher). But, that "surface" charge will quickly drop down to 12.7 volts (or so)... And then should fall slowly after than (depending on lots of factors, loads, battery capacity, temperatures, age of battery, any "issues" with batteries, etc.).

AGM batteries can be a "difficult animal" to manage. For Lead Acid batteries, the Specific Gravity measurements of each cell, are the "gold standard" for determining state of charge and how well they are being treated (properly charged, not over discharged, etc.). However, with AGM and other sealed batteries, you do not access to the electrolyte, so you cannot make those measurements. And voltage measurements of groups of cells, can be problematic to interpret.

You got 2x 6 volt cells in series on a 12 volt battery bus. That is "helpful" because you can, at least, compare how the two batteries are performing by measuring the voltage across each 6 volt battery (ideally, we would be measuring the voltage across each cell, but modern batteries make per cell voltage measurements pretty much impossible).

Many times, a battery's problems is caused by the failure of one cell... So, by measuring the 6 volt battery voltage over time and current (charging, discharging), you may find that the batteries have almost identical voltages, or you may find one battery with much higher voltage (during charging) and much lower voltage (during discharging)--That could indicate a weak or failed cell. (cells can fail open or shorted or have "less capacity" than the rest of the cells).

Unless you took the batteries "dead (well below ~11.5 to 12.0 or to 10.5 volts--which is "truly dead") and let them sit for days/weeks without recharging--I would be surprised if you "sulfated them"--That usually takes weeks of setting at partial charge (less than 75% of charge) without charging/cycling. (note, I am not a battery engineer--And I am making guesses from your writings here).

Also--For AGM batteries, in general, they usually are not charged >~14.4 volts at ~70F... If you charge AGM batteries >>14.4 volts, they tend to "gas" (generate hydrogen and oxygen). That can cause the batteries to vent (not a good thing, lose of gasses/electrolyte is permanent and eventually will kill AGM batteries). Also, high voltage+high(er) charging current cause the batteries to run "hot" (fully charged batteries turn excess charging current into hydrogen+oxygen+heat, and the recombination of hydrogen+oxygen back into water via catalyst also generates heat). Taking a lead acid battery >115 to 120F+ is not good. (keeping batteries hot also ages them quicker--For every 10C increase in temperature, batteries will have 1/2 the life). Note that pumping ~2.5% or higher rate of charge into a "full battery" can easily overheat the battery.

For AGMs, monitoring the charging current (at a "reasonable" charging current) will tell you when they are fully charged... Most of the time, when the charging current falls below 1% to 0.1% of current, the battery is "fully" charged (tail of the charging cycle).

I am not a battery engineer, and I do not work for Rolls.. But, you are correct, it appears that Rolls has "realtively high" charge voltage set points for their AGM batteries.

http://support.rollsbattery.com/support/solutions/articles/4345-agm-charging

As long as you monitor your battery bank temperature (IR thermometer for quick checks, wire in a "remote temperature gauge" for permanent monitoring may be nice)--That will help you have a longer battery life too.

In general, for longer battery life, we suggest not discharging (very often) below ~50% state of charge (50% of 250 AH is 125 AH). And never below 20% state of charge (battery/cell damage can occur).

A 1 amp ghost load can be a killer--That is 24 AH per day (assuming no charging current)--Or to 50% in ~5 days with no other loads, and 10 days without charging, to dead.

Assuming you have not done any of the "bad things" (take battery dead, let sit for days/weeks/months at less than 75% state of charge, overheated battery, over charged battery, etc.)--I would look very closely how the two 6 volt batteries respond to loads and charging currents. If one battery is "significantly different" than the other--I would suspect the battery with the "wider voltage swing" has issues (bad cell?).

The are other possible issues--If the two batteries were not fully charged when installed (but one battery was fully charged and the other at 50% state of charge--AGM batteries do not "equalize well/quickly" and each battery should be recharged on a 6 volt charger until both are fully charged). If you measure the voltage across each voltage before you installed them--That resting voltage can help estimate their initial state of charge). Ideally, you want both batteries to have near identical voltage before you install them in a series.

If the batteries both behave identically during loads/charging -- Then either both are bad, or something was done to them somewhere/somehow that killed.

I would suggest that if you cannot get any help/resolution from Rolls, your next set of batteries be a pair (or two pair) of 6 volt flooded cell golf cart batteries. They are much easier to monitor (hydrometer) and much more forgiving than AGMs. But you do have to check water levels once per month and keep them clean and the box vented--AGMs are "much cleaner". Once you get your system working with the "cheap" batteries for a year or so--Then AGM may be the next step (or other chemistry).

If you do not have one yet, a battery monitor can be helpful. However, I am not sure it would have helped with your situation.

Unknown battery problems are a huge pain. In some cases, it is the mfg's problem--in some cases, and many others, it is probably a customer caused issue... And it can be difficult to figure which it which.

Good luck,
-Bill

We are still "rattling" Vanilla's support team for a quote on the project. We are planning on getting that "upgrade" unless it ridiculously expensive.

-Bill

Unfortunately, having "archived" post numbers is going to be too expensive and complex for them to implement (and all of the merge/delete threads/discussions permutations). The post numbering will be "dynamic" (i.e., the numbering will be based on the thread/discussion displayed at that moment).

I delete so few posts in the middle of a discussion (hardly any a day or two later)--That it should not confuse anyone very often (almost never, my guess). If I miss a post number reference, somebody can always make a post and I will edit/fix in old post.

As an aside.. .I would have been OK if they would have "fixed" time/date for post ID. Currently, they go from "time" (posts less than 1 day old) to "date" to month over a few days (posts over a few days old simply say June 2016). Turns out that "fix" is "a lot" more expensive/complex fix than "dynamic" post numbering. I sometimes wonder if software engineers ever use their own product...

-Bill

Yes, Vanilla had good user reviews, and is hosted/managed by Vanilla (old forum software was hosted and managed by NAWS, with some help from VBB). Apparently VBB kept "improving" the software until nobody liked the present versions (and we could not go back to a few year old version).

And the other Vanilla reason for choice, was as you surmized Vic, that they would preserve the old posts/threads.

-Bill