For years, Flooded Lead Acid (FLA) batteries were the standard for deep-cycle RV batteries. The only decisions that needed to be made were 12-volt or 6-volt and how many Amp Hours (Ah) were needed. FLA batteries have lead plates suspended in electrolytes in individual cells and are the cheapest, but require more maintenance. They gas when recharging and require more distilled water to be added frequently. 6-volt batteries have three cells that produce 2.1-volts and require two batteries connected positive to negative, in series to create a 12-volt bank. This however does not double Amp Hours.
12-volt batteries have six cells, each producing 2.1-volts and can run a smaller rig with just one battery.
In the mid-80s Absorbed Glass Mat (AGM) batteries were being developed for the military as they were less prone to sulfation, required no maintenance especially distilled water being added, and lasted longer. They also have positive and negative plates and electrolytes however fiberglass mats are placed between the plates and absorb the liquid. AGM batteries started showing up in the RV world sometime in the late 1980s as the demand for 12-volt power grew. There were also challenges with placement and since the AGM battery is completely sealed there was no maintenance and no leakage. Plus the gases that are produced are kept internally rather than vented so they can be placed almost anywhere.
Lithium Iron Phosphate (LiFeP04) batteries have individual cells with no gassing and can be drained 100% of available amp hours. They do require a higher charging voltage and are much more expensive.
FLA and AGM batteries should only be drained to 50% Ah and discharging them lower than that will reduce the life expectancy. A fully charged FLA and AGM battery should read 12.6-volts and the misconception is a 50% drained battery is not 6.3-volts. Here is the discharge chart.
Voltage – FLA State Of Charge Voltage – AGM
12.6-Volts 100% 13.0-Volts
12.5-Volts 90% 12.75-Volts
12.42-Volts 80% 12.5-Volts
12.32-Volts 70% 12.3-Volts
12.2-Volts 60% 12.15-Volts
12.06-Volts 50% 12.05-Volts
11.9-Volts 40% 11.95-Volts
11.75-Volts 30% 11.81-Volts
11.58-Volts 20% 11.66-Volts
11.31-Volts 10% 11.51-Volts
10.5-Volts 0% 10.5-Volts
A FLA battery that is discharged to only 50% should last 300-500 cycles while an AGM battery can last 600-1000 cycles. Lithium Batteries can cycle anywhere from 2,000-10,000 and several of the high-line brands are guaranteed for 10 years and some even for a lifetime! If they are maintained and charged properly!
Proper Charging Profile
As an FLA battery is drained, sulfur coats the plates and needs to be conditioned or desulfated. A typical RV converter charges the battery at 13.6 volts until it reaches 12.6 volts and then drops to a maintenance charge of 13.2 volts. This does not break up the sulfation and the sulfation will thicken on the plates and the battery will not hold a charge or last as long as it is designed. FLA batteries require an initial bulk charge of 14 volts or higher and then an equalizing and float charge. Only a multi-stage charger will condition FLA batteries properly. This can be done with an inverter/charger or even a solar panel with a charge controller.
Winnebago Industries has worked with Progressive Dynamics to engineer their charger to put out 13.8 volts for 8 hours to condition FLA batteries. Other converters like the PD 9300 have programable charge profiles to customize the voltage for specific battery types.
The challenge with AGM batteries is every manufacturer seems to have a different charge profile and they can not agree on what is best. Recently I contacted my “Go To” guy at Progressive Dynamics and he stated that they have been working with battery companies and RV manufacturers for over 20 years trying to standardize charge profiles to best maintain batteries.
For example, the Go Power “Solar” AGM battery wants 14.4 V – 15.0 V for the initial charge then a float or maintenance charge of 13.5 V – 13.8 V. You can find the charge profile in the specification sheets.
Trojan Batteries require 14.4 V and a float of 13.5 V, and most don’t even give the parameters such as Interstate which is a popular replacement for RV owners.
What this means is that your typical deck-mounted converter/charger like this WFCO will not fully charge an AGM battery and could cause sulfation even though many brands advertise that AGM is not prone to sulfation!
Progressive Dynamics has introduced their 9300 Series which can be programmed for the different charge profiles.
Flooded Lead Acid (FLA) Mode
The patented Charge Wizard 4-stage system uses microprocessor technology to add intelligent charging capability. It constantly monitors the RV battery and automatically adjusts the converter output voltage based on the battery’s charge status – designed to eliminate battery over & under-charging problems associated with most other battery chargers and provide rapid yet safe battery recharging after dry camping. The Charge Wizard constantly monitors battery voltage and battery usage and then selects one of the following four operating modes to properly charge and maintain the battery. BOOST Mode 14.4 Volts – Rapidly brings the RV battery up to 90% of full charge. This mode is maintained for 4 hours. NORMAL Mode 13.6 Volts – Safely completes the charge. If light activity is detected after 33 hours in this mode, the Wizard switches to the storage mode. STORAGE Mode 13.2 Volts – Maintains charge with minimal gassing or water loss. EQUALIZATION Mode 14.4 Volts – Every 21 hours for a period of 15 minutes prevents battery stratification & sulfation – the leading cause of battery failure. This functions as part of the Storage mode
Absorbed Glass Mat (AGM) Profile
BULK Mode 14.0 Volts – Initial charge to 70% State of Charge. Occurring at startup, this procedure will last for 2 hours.
ABSORPTION Mode 14.7 Volts – Finish charge to 100% State of Charge. Running for a minimum of 1 hour, after which the converter switches to “FLOAT” mode when either the current drops below a preset limit or times out at 4 hours.
FLOAT Mode 13.6 Volts – Maintains charge. The converter will stay in this mode indefinitely as long as the converter has AC power. Once a week “DESULFATION” mode will activate for 1 hour then revert back to “FLOAT” mode.
DESULFATION Mode 14.7 Volts – Once a week for 1 hour to prevent sulfation and refresh the battery charge. This occurs as part of the “FLOAT” mode operation.
Lithium Iron Phosphate (LiFeP04)
Although the optimum charging voltage for the LFP battery is 14.6 VDC, many manufacturers are specifying a charge voltage of less than 14.6 volts and setting the high voltage cutoff at 14.6 volts through the Battery Management System (BMS). In general, this is not a user-adjustable function. Progressive Dynamics has run numerous tests at 14.4 volts showing that the battery can receive a full charge at the converter rating. Progressive Dynamics has developed a Lithium multi-stage charging profile with the ability to monitor the voltage and current. This allows the Charge Wizard to select the correct charging voltage as needed while providing DC power to the RV. These are automatic functions. The Charge Wizard will properly charge and maintain the battery while providing safe operating voltages within the RV.
CHARGE Mode 14.4 VDC – Initial charge to full. Automatically selected at start-up. After 1 hour and the current drops off, or 8 hours of charging has elapsed, the charger switches to
IDLE MODE. IDLE Mode 13.6v VDC – This is a nominal voltage for an RV connected to shore power. This mode is continuous but will revert to CHARGE if the power demand is high or AC power is reapplied.
REFRESH Mode 14.4 VDC – Occurring during IDLE mode. Once every three weeks, a charge voltage is applied for 1 hour to refresh the battery.
So to get the ultimate life out of whatever type of deep cycle battery you have or looking to replace your existing battery with, it is important to do a little research regarding what voltage is required for initial charging and the charge profile. Some of the “big box” store batteries don’t show a charge profile or any other information as they don’t want your batteries lasting 5-7 years, rather see you come back in 2-3 years and buy more batteries. You really do get what you pay for!
About the author: Dave Solberg: Managing Editor, RV Repair Club
For the last 25 years, Dave has conducted RV maintenance and safety seminars, developed dealer and owner training programs, written RV safety and handyman articles, authored an RV handbook reference guide and logged over 100,000 miles on the road in an RV.
RV Repair Club is your go-to online resource for enthusiasts who want quality RV maintenance, repair, and upgrade information – a community where passionate RVers can come together to gather knowledge and share their experiences.
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Thanks for the great guide! Understanding the correct charging profile is critical for battery health. Proper charging extends lifespan, improves performance, and prevents damage. Very helpful tips for all battery owners.