When two batteries are wired in parallel, all charging sources and Loads should attach to the (+) of one battery and all (-) charging sources or loads to the other battery. If both load/charge cables goto just one battery, that battery has to work significantly harder, and will degrade faster.
Watch this:
The batteries in this topic have just crossed that 'Just Fine" and 'Still going strong" grey area into the 'Hmm something is wrong what do I do?' Area.
For most everyone, it is one or the other, and no In between.
These batteries need some intense charging to attempt to restore Specific gravity up to the 1.275 level, or higher.
No low and slow solar is going to do it, you can't try and continue cycling these batteries until they are recharged, and an attempt is tried to get specific gravity up. Your only hope of making them last another 6 months, is with an Equalization cycle, and better recharging practices if they do respond to the Equalization.
First,
If the cells are low on water, fill them with distilled water, but only enough to cover the plates and 2MM or so above, not all the way full.
Ideally, Each 12v flooded battery should be individually put on a charging source, of no less than 10 amps until battery voltage rises to 14.8, or there abouts.
There is the possibility of a shorted Cell. One should unparallel the batteries and see if one jumps back upto ~12.0 in an hour or so, and the other stays at 10.5. if this is the case, Do not try and attempt to recharge the 10.5v or less battery.
There is also the possiblity of one cell giving up only under load. The battery under a minor say 3 amps load might drop to 10.5v or less, and instantly rebound to ~12.x when the load is removed. I had one 12v battery die this way. If the battery behaves like this, make no attempt to recharge it.
Often if one cell in a pair of 12v batteries in parallel fails, the reduced capacity is not noticed until the other battery degrades, and it will degrade much faster when paralleled to a battery with a shorted cell. The sooner you can remove the battery with the shorted cell from a paralled bank of batteries, the better.
6v GC batteries in series will not kill each other if a cell shorts, but it will only be a 10.5v nominal bank of batteries and the 5 other cells will work much harder. Unfortunately one should not just replace one 6v battery when it fails, but replace both.
After the 10 amp plus charging source has gotten the battery upto 14.8v for 2 hours, then one needs to perform an Equalization charge on the battery. One needs at least 5 amps to push a 100 amp hour battery up to 16 volts. Battery Voltage should not be allowed to exceed 16 volts. A hydrometer, NOT the useless floating ball type, or the plastic type, but the Glass turkey baster style with glass float like the OTC 4619.
All 6 cells should be dipped and readings recorded. Make sure no bubbles stick to the float when taking a reading.
One is hoping to see 1.275 or higher, but do not be surprised to see 1.215 or less, EVEN AFTER after the battery was held at 14.8v for 2 hours or longer.
After this 'full' charge then one needs to be able to bring the battery up to an even higher voltage.
When one applies a charging source which is trying to bring the battery upto ideally 16.0 v but a minimum of 15.5 volts, the battery will gurgle and bubble, and start to warm up slowly. This is where one is trying for force the lead sulfate back into the electrolyte, and heat is a good thing, the bubbling and gurgling are a good thing too as it is stirring the electrolyte and trying to abrade the sulfates occluding the plates.
But do not let the battery exceed 120 degrees F. Stop charging when Specific gravity no longer rises. Also to note is SG readings are efffected by temperature. The level on the float might not keep rising, but when the temperature rise is factored in, it is still rising.
The OTC hydrometer:
http://www.amazon.com/OTC-4619-Professional-Battery-Hydrometer/dp/B0050SFVHO
has a little thermometer on it which will say to subtract X amount or add X amount depending on temperature. It takes while for the rubber base to come up to temperature. The cells on the interior of the batteries will warm up faster, so take this into account too when writing down readings.
One can just dip the weakest cells instead of all 12 every time, but one should check SG every 15 minutes. This can take upto 6 hours
If all the cells get up above 1.270, congratulations you might easily get 6 more months from them. If one or two remain under this point, all is not lost. They could last a bit longer with a weak cell or two.
If they do not respond, then start searching for batteries. Often Golf courses sell or just exchange their GolfCart batteries when they only have 80% or their original capacity, and one can still get many cycles from these in rv use. They are also a good place to get new batteries from when they place a large order
Yes, Equalization is a rather involved procedure, and No it is not easy to obtain a charging source that can bring a battery above 15 volts.
One can wire their 100 watt or greater solar panel directly to the battery terminals, but the battery cannot have anything else attached and not allowed to exceed 16V. It should be allowed to sit at 14.8 for two hours before being pushed upto 16V.
Some charge controllers allow the voltage to go this high. Remove all loads on an individual battery and let the controller do 14.8 for two hours then reprogram it as high as possible, upto 16v. Obviously one needs good sun and preferably 6 hours of it.
RV converters cannot do an Equalization charge, though some make this false claim. RV converters are a cause of premature batter failure as they do not go to high enough voltage or hold it long enough. Too long and too thin of wiring is a big contributing factor for poor converter performance. Upgrading the copper is beneficial in more than one way for not only minimal voltage drop, but for allowing the converter to hold the higher voltage for longer, as the battery wants 99 times out of a hundred.
Some Automatic battery chargers can do 16 volts. Some do it even when it is not desired. Old school manual chargers can do it, but slowly, and need to be monitored, and it might take days.
Most of my posts in this electrical forum are to keep this situation happening in the first place. As batteries get worked they lose capacity. As they lose capacity, and one does not lessen their amount of electricity required, the batteries are in fact being cycled deeper and deeper, in terms of percentage. As they get cycled deeper and deeper they get damaged even faster, and at some point they just give up, murdered.
Proper battery charging can greatly extend the lifespan of batteries. Monthly Equalization charges can easily double battery life when the battery is cycled each and every day.
It that worth it to you?
When performed every 30 cycles, the procedure takes much less time and need not be monitored as closely.
If one wants to know how to simply turn a dial and bring a battery upto 16 volts when grid power is available, check out 'my newest electrical toy thread'.
https://vanlivingforum.com/Thread-My-newest-electrical-toy
Those relying on generators, can really benefit from such an adjustable voltage power supply as it will hold the battery at whatever voltage you choose for as long as you choose to run the generator. An RV converter will decide to lower to float voltage prematurely, to the serious detriment of the battery.
Only Lifeline AGM batteries condone and recommend a 'conditioning' procedure, which is similar to an Equalization cycle on a flooded battery.
Other AGMs will not say it is recommended and say to not attempt, but with careful management and observation, can be done too in an attempt to wake up an abused AGM battery to get some more service from it.
Read Lifeline's tech sheet PDF closely and do not exceed their recommendations, if one want to attempt to 'condition', any other brand AGM.
Thermal runaway is a valid concern and can have consequences.
http://www.lifelinebatteries.com/manual.pdf
I know that those wheeled chargers at Auto mechanics certainly look impressive. Often, they are not. Restoring maximum specific gravity is not as easy as just slapping on an impressive wheeled charger.
My 'newest electrical toy' is a fraction of their size, and more powerful and more effective than most any of them.
