Any chance you just depleted the batteries much further than normal?
Your wording leads me to believe you are misinformed about battery charging.
Achieving 14.2v is not an indicator that you have reached full charge.
Batteries, as they are charged, have their voltage rise, but once a certain voltage is achieved, does not mean they are fully charged.
The Bulk Phase of charging is pretty much when the battery is thirsty and can gobble up nearly any reasonable current you can feed it. During bulk phase, voltage will rise from anywhere from below 12.8 volts to the mid 14's. The alternator can be, if wired correctly, a very effective bulk charging tool.
Usually the bulk phase ends in the 80% charged range. Applying bulk currents into a battery at 80% charged or above will cause the voltage to exceed the safe voltage regulation setpoints. From 80%+, time and decreasing currents are needed to safely squeeze in the last 20%.
Anybody who claims they can fully 100% recharge a deeply cycled lead acid battery in a few hours or less is smoking crack or just plain ignorant of battery charging.
Do not believe charger documentation that says X hours to full. These claims are ridiculous as they usually do not even state what size battery nor how much it is depleted, nor even what they are considering "full".
Different chargers/controllers have different setpoints programmed in, but these setpoints are likely more influenced by lawyers and bean counters than engineers.
The acceptance/absorption voltage is when the charger/controller allows the voltage to climb no higher. The amps required to hold the battery up in this range will taper down in to the 1 amp or so range, depending on the size and health and construction/design of the battery. This can take 45 minutes to several hours of this constant voltage "acceptance/absorption" phase of battery charging. This stage is the most important for returning the battery to full energy density.
Most chargers, after a preset time limit, or when current required to hold 14.x volts drops below a certain threshhold, will at this point revert to float (13.2 to 13.6v)mode. They consider the battery fully charged at this point, but in reality it is more like 92 to 95% charged. Which is what the lawyers want, as it is safer to undercharge a battery than to over charge it, and lawyers are not concerned in the least about the long term health of your battery.
Now when controllers do not allow the user to select the acceptance voltage, and decide 14.2v is plenty, they are doing a disservice to their customers. Batteries like trojans absolutely need 14.8 volts acceptance. My USbattery wants a 15.3v "finishing" charge after a 14.45v acceptance charge lasting several hours.
My Flooded USbattery specific gravity will not return to 1.280 unless I program my solar acceptance voltage to 15.9v, and it takes 2+ hours to achieve this. This is achievable only after the acceptance/absorption phase has held the battery at 14.6v for a few hours. I need strong sun and enough time to do it.
My recent Solar setpoints are 14.6v acceptance and 14.7v float. The amps required to hold a 14.7 float after several hours at 14.6v is about 0.3 amps. One might think these setpoints are too high and I am overcharging the battery, yet after 2 weeks of doing this, and enough sunlight to hold these setpoints for a few hours daily, my temp compensated hydrometer reveals Specific gravity readings in the poor to fair category. 1.220 to 1.250. Meaning I was not fully charging the battery daily despite the high voltage settings and the soothing flashing green light.
Every two weeks I have to reset my acceptance and float voltages to the high 15's to return specific gravity af all cells to the 1.280 baseline. The battery after this equilization/ intentional overcharge, performs much better the first few nights. I judge this by voltage held for amp hours removed, and have the tools to accurately measure this.
One cannot test the Specific gravity on AGM batteries, so one cannot really see how their charging regimen is affecting their battery. If the charging regimen is poor, the owner finds their pants around their ankles at some point.
The Gist of all of this is, is that voltage is a poor indicator of state of charge.
A blinking green light does not mean the battery is indeed fully charged.
Achieving 14.2v does not mean a battery is fully charged. Holding 14.2v for 6 hours might not get the battery to full charge.
Battery longevity is directly related to how well the battery is returned to a true 100% full charge ( or as near as possible) every 7 to 14 days, when cycled daily, and how well the user can actually achieve that. The more often 100% is achieved, the better.
The battery manufacturer has a charging regimen to best return their batteries to maximum energy density. This info is not always easy to find. I will not buy a battery unless I can find this info.
They will usually list a minimum and perhaps maximum bulk current, an acceptance voltage, perhaps a duration at acceptance voltage, then a float voltage. Very few chargers/controllers out there will meet these recommendations. They are hamstrung by the lawyers and likely the bean counters too, and rely on their savvy marketing department and customer's ignorance about proper battery charging, to sell products.
Also the old wives tales of battery charging are still espoused and this is usually the "trickle charging is best" mentality. Low and slow( trickle) might be the least damaging way to fully charge a battery if one has several days to allow the battery voltage to slowly climb, but the fact is that in actual application, the battery voltage needs to climb to the mid 14's and be held there for several hours to squeeze in all the amps the battery can take, and a 13.6v "trickle" charger will never do this.
Some batteries, like some AGM's, require a minimum bulk current be met, meaning if you just do grandpa's recommended "trickle" charge on them, it is likely the best way of killing a battery short of depleting it fully and allowing it to freeze, or just taking a shotgun to it.
Batteries are not just ubiquitous as to their charging requirements. Just Any charging source is not going to ensure the battery gets fully and properly recharged, but ANY charging source, is better than NO charging source, on a depleted battery.
Proper Recharging a cycleable battery on a daily basis is much, much different than what a starting battery requires to hold it near full charge, where it was designed to live and what vehicular charging systems are designed to do from the factory.
The better one can meet the manufacturer specified charging regimen on a deeply cycled battery, the better the battery will perform and the longer it can perform for. It is not always easy to find or meet these charging specifics, but ignorance of them is akin to shooting oneself in one's foot.
Now if one cannot be bothered with going through the effort of attempting to meet the battery manufacturer charging recommendations, then they have to accept that they will not get the lifespan expected from the battery. After all it's only money, and spending more than the battery costs just to charge it correctly, well one must consider the return on investment, and put a price on their time and stress on dealing with the correct charging of their batteries.
Some can't be bothered. Ignorance can be bliss, until one awakes to a warm fridge or an inverter alarm, and only then decides that the battery was perhaps not getting charged correctly and now cannot hold enough electricity to meet their overnight needs.
So at this point the battery user gets a new battery and treats it the same, or they try to treat it better.
Those in the latter category should read all they can about proper battery charging. Those in the former category should not espouse their methods or ignorance or prolong the old wives tales of Lead Acid Battery charging.
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery
