For those using Odyssey batteries or any battery that is the same. Info is from Odyssey;
ODYSSEY Battery basics… ODYSSEY batteries are an AGM Lead Acid battery however the TPPL (Thin Plate Pure Lead) technology requires that the batteries be charged at a higher amp than most batteries and maintained at a slightly higher voltage than other standard lead acid batteries on the market. They are also truly dual purpose batteries that can be used for both cranking and deep cycling. Due to the technology, proper charge maintenance is critical to maximizing the life and performance of the ODYSSEY battery.
Most conventional batteries are considered fully charged at 12.6-12.7V. The ODYSSEY TPPL AGM battery is not considered fully charged unless it has a resting voltage of at least 12.84V. The usable energy of the ODYSSEY battery is from 11.2V (0% state of charge) OCV to 12.84V OCV (Open Circuit Voltage should be checked 8 – 24 hours post charge with no loads). When the battery goes below 10.0V OCV it is over discharged and is getting into the chemical part of the battery and can cause permanent damage. At less than 10.0V the ODYSSEY limited warranty deems the battery over-discharged due to abuse or neglect (usually unintentional). The ODYSSEY charger/maintainer or any approved maintainer can maintain the ODYSSEY battery indefinitely in or out of the application provided it has enough charging current to counteract the parasitic loads of the application. If the battery becomes over-discharged (below 11.0V OCV) then the sooner the battery can be fully charged the better. If the battery remains connected to the application during storage or extended periods of non-use, to prevent over-discharge and maintain the battery at a full state of charge, an ODYSSEY program approved maintainer would be required and/or disconnecting the battery prevent over discharge. There is a link to a list of ODYSSEY approved 12V chargers located on the ODYSSEY website Literature page for your reference.
The list of approved 12V chargers is provided due to the many chargers that are programmed for the vast majority of batteries on the market that prefer low amp charging and lower float voltages that do not fully charge or maintain the ODYSSEY battery properly. The minimum recommended charging current for an ODYSSEY battery is 40% of the 10 hour amp hour rating of the battery for cyclic or deep discharge applications (for example about 3A for a single 8Ah rated PC310 for example), a constant float voltage of 13.5-13.8V and no constant voltages exceeding 15.0V in any kind of de-sulfation/reconditioning/equalize mode. At greater than 15.0V the battery can overcharge, overheat, and/or go into thermal runaway. Maintaining any ODYSSEY battery at less than 13.5V will bring the battery down and maintain it in an undercharged condition causing sulfation and premature failure. This would not be considered a warrantable manufacturing defect failure.
For seasonal applications (non-daily use applications that set for more than 3 days in a row frequently) regular use of an approved maintainer that meets the charge voltage requirements noted in the previous paragraph is highly recommended during the season and/or a disconnect switch. The preferred storage method is to fully charge the battery before storing and disconnect the battery from the application (shelf storage mode). Stored in or out of the application with no loads, the battery would not require charging for up to 2 years at 77°F or until it reaches 12.0V, whichever comes first before charging is required. The self-discharge rate increases significantly for temperatures above 25°C (77°F) and for every 10°C (18°F) temperature increase the storage time to recharge is decreased by half. Charge maintenance is critical to maximizing the life and performance of the battery. Freezing will not harm the battery and self-discharge rates reduce significantly at colder temperatures.
It is recommended that the ODYSSEY battery be charged if it is less than 12.65V (about 80% state of charge) when put into use as a cranking battery per the ODYSSEY Owner’s Manual (link provided on website Literature page for your reference). Most standard alternators are meant to top off a slightly discharged battery and maintain a fully charged battery. Most standard alternators/stators are not meant to be deep discharge recovery chargers and can become damaged if consistently used like one as well as not fully charging the battery with limited use. A battery discharged to below 80% capacity may not reach a full state of charge, regardless of how long you drive the vehicle using a standard alternator. Typical alternators only run at full amp output for a very short period of time before reaching its charging voltage and dropping into a very low amp trickle charge. Luckily enough, ODYSSEY batteries are very efficient at accepting high amp charging for quick charging.
Low amp trickle “charging” a discharged ODYSSEY battery is very inefficient and also causes premature sulfation. With the use of a 3A or higher amp charger that does not exceed 15.0V, the PC310 battery for example, should charge to a high state of charge (at least 85% SOC) then, an approved lower amp trickle maintenance charger should be able to complete charging process without prematurely sulfating the battery. The Cyclic Charge Voltage range printed on the top label of the battery is the recommended voltage at the battery from the applications charging system (alternator or stator). At less than 14.1V the battery may not be getting fully charged for infrequently used applications. You can verify the battery voltage by checking the voltage at the battery at least 8 hours after application use (or off charge) and if the battery voltage is not at least 12.84V then the battery is not considered fully charged. Voltage readings taken right off charge or after use (alternator/stator charging) will be inflated and inaccurate so for a true OCV reading, you should wait at least 8 hours before checking the voltage (OCV) with 24 hours being preferred.
Any lower amp (less the 3A for PC310 for example) charger that floats between 13.5-13.8V at the battery and never exceeds a constant voltage of 15.0V in any kind of automatic reconditioning, equalize, de-sulfation mode can be used as a maintainer only provided the charging current is high enough to counteract the parasitic loads of the application and maintain the acceptable voltage in float mode at the battery. With proper charge maintenance, a comparable Ah rated battery should have a service life of 2-3 times that of the same sized (Ah rated) battery in the same application with the same usage. ODYSSEY batteries have an 8-12 design life and have been known to function successfully well past the design life of 12 years for UPS applications where the battery is maintained at all times. Here is the link to the program approved charger listing from the ODYSSEY website Literature page for your reference. http://www.odysseybattery.com/documents/ODYSSEY_approved_12V_chargers.pdf.
http://www.odysseybattery.com/documents/ProceduretorecoverdeeplydischargedODYSSEY.pdf deep discharge recovery procedure to fool a charger with a low voltage safety feature that prevents charging what appears to be a 6V battery at less than 7-9V on a 12V charger or charger setting.
http://www.odysseybattery.com/documents/ODYSSEY_Battery_Reconditioning_Charge_Procedure.pdf reconditioning cycling procedure to reverse sulfation and recover capacity and cranking amp from improper charge maintenance.
For deep or over discharge recovery, I recommend charging the battery with a high current charger that does not exceed 15.0V as many times as it takes for the battery to take and maintain a charge without overheating. 8-10 hours a day with an overnight rest. If overheating to the point of venting or you cannot hold your hand on it occurs, discontinue charging and allow to cool completely for 24-48 hours before attempting to charge again. If this situation repeatedly occurs when the battery voltage on charge is not exceeding 15.0V then the battery is severely sulfated from being in a deeply or over discharged state too long and is no longer recoverable. The reconditioning cycling procedure (manual de-sulfation 2nd link above) should be performed at least 2 times (assuming the battery is taking a charge, not overheating during charging, but is not performing well). Improvement would be indicated with longer run times with each successive discharge to the same discharge cutoff voltage under the same loads. Discontinue cycling once the discharge time remains the same for two successive discharges. The longer the battery remains in a deeply or over discharged state, the harder it will be to recover.