Guide to 12-Volt Batteries: Everything You Need To Know
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Guide to 12-Volt Batteries: Everything You Need to Know
In this section, we will provide a course on the various types of 12-volt batteries. We will discuss cranking/starting vs. deep cycle batteries, the quality of batteries based on amp hours, their advantages and disadvantages, and groups (or sizes) so you can choose the best battery for your needs.
Cranking Batteries and Deep Cycle Batteries
Cranking/Starting Battery &#; The cranking or starting battery is used for quick and powerful bursts of energy to start an engine. The more inside lead plate surfaces the better for providing quick bursts of high energy. Many thin lead plates provide the necessary surface area. Pitting and warping, while appearing as a bulge in the lower portion of the battery, occur when cranking batteries are repeatedly discharged and recharged. Cranking batteries are available in flood lead-acid and absorbed glass mat (AGM).
Deep Cycle Batteries &#; The deep cycle battery is designed to operate over a long period of time with charging cycles done between the long discharge cycles. Deep cycle batteries have fewer, thicker lead plates that are much less likely to overheat during their long discharge cycles. Deep cycle batteries are designed to be discharged and recharged often. They are available in flood lead-acid, absorbed glass mat (AGM) and Lithium Iron Phosphate (LiFePO4).
Amp Hours &#; Each 12-volt battery has an amp hour rating or a cold cranking amp rating. The amp hour rating defines how many amps the battery can provide for what length of time. For instance, a 100 AH rated battery can provide energy to a 20 amp draw motor for 5 hours (100 / 20 = 5). Using a battery with a higher amp hour rating, you can operate that same 20 amp draw motor for longer. If you can&#;t find the amp hour rating on a battery, but you do know the Cold Cranking Amps (CCA), a general rule of thumb is to divide the CCA by 7.25 to determine the approximate amp hours of the battery. For example, if your battery is rated for 650 cold cranking amps, the approximate amp hours of the battery is 90 amps hours (650 / 7.25 = 90). The original amp hour rating on the battery will diminish with age.
Battery Types &#; Flood Lead-Acid, Absorbent Glass Mat (AGM) and Lithium Iron Phosphate (LiFePO4)
The job of a battery is to store and provide energy. The most commonly used types of 12-volt batteries are lead acid batteries, AGM (Absorbent Glass Mat) batteries, and lithium batteries. Most come in either a cranking (starting) or deep cycle design. Each type has its own unique characteristics and applications.
Flood lead-acid &#; Flood lead-acid batteries are the most common, readily available, and least expensive 12-volt battery available. They have been around for many years. Their voltage comes from a chemical reaction between the sulfuric acid and the lead plates within the battery.
Pros of a Flood Lead-Acid:
The flood lead-acid battery is the least expensive 12-volt battery on the market. They start at approximately $100.
In a cranking/starting configuration, flood lead-acid batteries are a great option for engines that require a quick burst of electricity to start. In a deep cycle configuration, they are effective at running equipment that draws less amperage for longer periods of time.
It can be charged at a temperature below 32 degrees.
Cons of a Flood Lead-Acid:
The life of a flood lead-acid battery is approximately 2 to 5 years.
The lifespan can be affected by hot or cold temperatures, the draw down (discharge) rate, depth of discharge, and the charging process.
They require the maintenance of keeping the liquid levels in the battery above the lead plates. Flood lead-acid batteries need to be used, stored, and charged in an area that is vented.
As the battery is being used, the flood lead-acid battery&#;s voltage lowers gradually until there is not enough voltage to run your piece of equipment. It is recommended that only 30-50% of the available battery energy is discharged before recharging. Continual deep discharging of a lead-acid battery will result in premature failure.
The lead plates are prone to sulfur buildup, which doesn&#;t allow the acid to contact the plates, reducing the effectiveness of the battery until it ultimately fails.
They weigh 40 to 50 pounds.
Absorbent Glass Mat (AGM)
The AGM battery is a more advanced type of lead-acid battery, developed in the early &#;80s. There is a fiberglass mat between the positive and negative lead plates that &#;absorb&#; the sulfuric acid so it isn&#;t sloshing around in your battery case. The case is sealed.
Pros of an AGM:
In a cranking/starting configuration, AGM batteries are a great option for engines which require a quick burst of electricity to start. In a deep cycle configuration, they are effective at running equipment that draws less amperage for longer periods of time .
They offer up to an 80% depth of discharge rate.
They will reach full charge up to 5 times faster than a flood lead-acid battery.
It can be charged at a temperature below 32 degrees. Their lifespan and effectiveness are not affected nearly as much by hot and cold temperatures, compared to flood lead-acid batteries.
Since AGM batteries are sealed, they generally do not require the maintenance that flood lead-acid batteries require.
They can be placed on their sides and can be mounted in areas that are not vented, providing flexibility in mounting locations.
They provide good shock and vibration resistance.
Cons of an AGM:
Lithium Iron Phosphate (LiFePO4)
LiFePO4 is a sub-type of lithium-ion batteries that are safer, have a wider use temperature range, and allow for many more charging cycles. Lithium-ion batteries were invented in the early s, and the first commercialized battery was sold in . In the past 10 years, the popularity of lithium-ion batteries has grown and their price has dropped. The battery is made of an anode, cathode, separator, electrolyte, two current collectors and a BMS (battery management system).
Pros of a LiFePO4:
LiFePO4 batteries provide high energy and a long lifespan (approximately 10 times the number of charging cycles of a lead battery&#; to 10,000 cycles). They generally last 6 to 10 years or more.
They can be charged with a higher amperage battery charger (approximately 50 amps), so they are capable of charging at a much faster rate than other batteries.
Unlike lead-acid batteries, LiFePO4 batteries do not gradually lose voltage during discharge, but rather maintain their voltage though their discharge cycle and then abruptly stop. The maximum discharge depth is generally 98 to 100%.
They contain a battery management system (BMS) that protects them and monitors the battery&#;s voltage, charging parameters, temperature, etc. A good BMS provides temperature protection, smart cell balancing, a communication module, a Bluetooth module, electronic switch, a self-heating module, battery parameter monitoring, battery discharge management, and more.
They may be cheaper in price in the long run when considering the long life of the battery.
LiFePO4 batteries have a high energy to weight ratio. A 12-volt LiFePO4 battery (100 AH) typically only weighs 20 to 30 pounds.
They are considered environmentally friendly.
Cons of a LiFePO4:
LiFePO4 batteries are more expensive ($200 to $) upfront and more complex than other types of batteries.
LifePO4 batteries are not recommended for cranking/starting applications.
Some BMSs do not include all the available protection and monitors. LiFePO4 batteries can require extensive research in order to get the right battery for your needs.
Most LiFePO4 manufacturers recommend an operating temperature range of -4 °F to 140 °F, and a charging range of 32 °F to 131 °F. If you charge outside of the manufacturer&#;s recommended range, you are likely to damage the battery severely and permanently.
LiFePO4 batteries require a special battery charger.
LiFePO4 is not considered a fully mature technology.
Group Sizes of 12-Volt Batteries
Group sizes and categories are used to classify 12-volt batteries based on their physical dimensions and terminal placement. These group sizes ensure compatibility with specific vehicles or equipment. Here is a list of a few of the common groups and sizes:
Group 24 10.25&#; x 6.&#; x 8.875&#; Available in 70 to 85 Amp Hours
Group 27 12.&#; x 6.&#; x 8.875&#; Available in 85 to 110 Amp Hours
Group 31 13&#; x 6.&#; x 9.&#; Available in 95 to 125 Amp Hours
(Batteries are also available in group 34, 35, 51, 65, 78, 8D, etc.)
Golf Carts batteries are typically made better and have thicker lead plates.
I decided to write this article because 75% of the people I help have the wrong battery for them installed in their RV. Your battery must state the AH (Amp Hour) capacity on the label or it is not a deep cycle battery. Most of these people went to an RV Dealer where they have a rack of batteries and you get to pick a pretty one. This article will help you find the best functioning battery for your RV, the way you use it.
If your RV is plugged in most of the time.
For people that keep their RV plugged in at RV park or home all most all of the time only replace battery when non functional. Try to find a battery with same physical size making sure to choose one with an AH rating on it. Each battery will have a capacity around 100AH. Scroll down to Brands.
Why is the RV battery Critical?
While boondocking our battery has many important tasks to do for us, some will be surprised how much we rely on them. The devices that require 12v power include Propane fridge controller, furnace thermostat and blower, lights, water pump, radio, move the slides, tounge jack, some leveling systems, many awnings and various others devices. Of course we can&#;t forget about starting the generator either, if you have one onboard.
Physical Size
This can be critical, your RV came with battery compartment or box and a venting system. It will be easier, but not always required to have your new batteries fit in same boxes. Flooded lead batteries will require adding water, checking the specific gravity and the venting system will have to remain functional. When measuring the battery box don&#;t forget to leave yourself enough height for connecting the battery terminals. If you decide to go with AGM or Lithium you have the ability to bypass the venting system, some mount them in living quarters for smaller temperature swings.
Types of Batteries
There are 3 main types of batteries, Flooded, AGM and Lithium in order of price. Flooded batteries are budget oriented and come with some Maintance and need to be vented. AGM is a sealed battery with no Maintance and more flexibility for mounting, no need to vent this type. Lithium can look more appealing than AGM with longer life cycles, more useable capacity and much lighter. The biggest downfall being temperatures below freezing. RV Battery Types &#; Lithium, AGM and Flooded.
Capacity of the Battery
Battery capacity is measured in AH&#;s. If your RV lights use 4A @ 12v and you leave them on for 2 hours (4×2=8AH) you will have used 8AH from your 12v battery. You will need at least 100AH of useable battery.
Venting
Capacity AH
Useable AH
Weight
Deep Cycle
Yes
100
50
60#
Deep Cycle GC
Yes
100
80
70#
AGM
No
100
50 &#; 80
70#
Lithium
No
100
100
30#
As you can see from the chart above, the GC (Golf Cart) batteries and some AGM batteries can let you use more of the capacity. This is because these batteries are made with thicker lead plates.
Lithium is a separate group, it is the newest battery type with a lot of potential. They can achieve - cycles in a laboratory! If your leaning towards Lithium, more information here. Is Lithium Right for my RV?
The chart below is chart of Lifeline AGM battery in a laboratory at a constant 77 degrees. The curve of the cart in relation to DOD (Depth of Discharge) is similar with ALL batteries. Most boondockers will be lucky to see 1/2 of this life in the real world with temperatures being an issue and not able to charge the battery consistently because of cloudy and rainy days. When the expected life cycles of a battery is over it will not be able to hold 80% of rated capacity. An example of that would be a 100AH battery only able to yield 79AH of energy.
Lifeline Battery
Charging
If you are boondocking, you will be charging with generator/converter or with solar. The converter does not charge Flooded or AGM batteries correctly. How do I charge my RV batteries? It does not have the ability to adjust voltage to exact battery specifications or correct voltage for the temperature of the battery. Lithium will loose capacity sitting fully charged from constant converter charging.
Some out of the box ideas for charging batteries will include jumper cables from truck battery to RV batteries and an inverter powered by truck alternator/batteries plugged into RV shore power. IMO these are acceptable to get you by in a pinch.
How many batteries do you need?
Conservitive minds with daily use of 100AH believe you should have 300-600AH of battery capacity(180-360 pounds of lead acid batteries!) This will allow you to get through rainy and cloudy days with no issues. Most of the time you will charge your batteries back up with only using 10-20% of your capacity. This will get you batteries to last much longer but you will spend more on them initially. With lead acid batteries you will also get a higher self discharge ~.6% daily to figure in. Many will be ok without a generator with the bigger battery. This is uncommon solution for RV because of weight and space.
Liberal minds with the same daily use of 100AH believe you will be fine with 100-200AH of battery capacity. This will get still get you through a couple of cloudy or rainy days and generally will have a little more solar capacity. Some may need another way to charge besides Solar, have for this setup and the battery will only have to get you through the night.
Most people in an RV will lean towards the liberal mindset with weight, size and price being biggest factors. If you want to use inverter to run microwave or AC unit things will change drastically. Yes, you can run an AC unit in an RV, I can run mine all night on battery alone. This is not the common set up in an RV yet.
This is my typical useage in my ATC Toyhauler RV.
ATC 28&#; FB
12v Amps
Hours run
AH
Trace Current
0.2
24
4.8
Garage Lights &#; 6
2
3
6
Kitchen Lights &#; 4
1.3
5
6.5
Entry Light &#; 1
0.3
1
0.3
Bedroom Light &#; 2
0.6
1.5
0.9
MaxxAir fan Level 1
0.1
4
0.4
MaxxAir fan Level 5
0.7
8
5.6
MaxxAir fan Level 10
3.2
2
6.4
Water Pump
6
0.75
4.5
Furnace Blower
7
2
14
Awning Led Light
1.1
5
5.5
12 volt Fridge *
3.3
10
53
Water Line Heater
~3
Fresh Tank Heater
~10
Gray or Black Heater
~5 each
Total AH per day
107.9
The first thing that sticks out is my 12v fridge consumption. This is not normal, the propane fridge will use 2-3AH per day.
Explanation of chart:
The trace currents could be propane gas detectors, a propane fridge (needs 12v to operate), thermostats or other devices that may have been installed. I would expect this exact current to be a moving target and be different on every RV. The number after the lights are the number of LED bulbs/pucks on each circuit, each bulb/puck seems to consume .3A. I have a 12 volt fridge that I installed aftermarket. Stock (from the dealer/manufacturer) is AC/ propane, which actually does needs 12 volt function. The heaters on my &#;3 season package&#; and the actual amperage used seems to vary and will depend on ambient temperature.
Once you take off the 53AH for the 12v fridge and factor in smart device charging and TV useage, this chart might be pretty close for most people.
Full Time Boondockers
For people off grid like me, the Battery, Solar and weather all have integral parts into the equation. I try to follow the 70 degree weather to keep my AC useage at little to none, plans of mice and men&#; The Battery has to be big enough to skip a full day of sun. The solar has to produce enough to charge the batteries in winter, with low and short sun days. Can you run AC from solar and batteries?
Battery Brands
A budget value lead acid battery is made by East Penn Manufacturing. They make Flooded and AGM batteries with Deka and Duracell brands Deep cycle batteries in Pennsylvania and Iowa. Trojan T105 Deep cycle batteries are a little more money with a tried and true great reputation. Trojan and Crown have AGM versions as well and typically will be twice the price of flooded version. Lifeline makes a industrial AGM battery that in my opinion is second to none. Rolls Surrette is in this elite class as well.
Lithium Geek Speak
The two main Lithium chemistries that are of interest to me are NCA (Lithium Nickel Colbalt Aluminum oxides) and LPF/LiFePO4 (Lithium-ion Phosphate). There are many more and there will be more to come before we find the Holy Grail of batteries. All Lithium batteries will need a BMS (Battery Management System). This will protect the battery from temperature and voltage. If this is not done correctly it can end with a junk battery or an exploding fiery mess!
Lithium NCA can be found in our laptops, phones, cordless tools and most Tesla&#;s use this chemistry as it is significantly more dense at ~250Wh/Kg. These are made by Panasonic and LG and some are produced here in the states. This is the least stable Lithium battery and needs to be monitored well with a good BMS. Tesla is leading and changing the rules in the Lithium Battery world. They designed the primary cell for the Model 3 and now it is in all high end power tools. Yes my RV is powered by Tesla Batteries. I love watching Tesla and how they are changing the battery world as we know it!
LiFePO4 has a density of ~100Wh/Kg and this is what is used for RV drop in replacement batteries. All Lithium primary cells for RV drop in replacement batteries are made outside of the US and most/all come from china. This chemistry is much more stable but still needs a good BMS to protect it. BattleBorn is US company that assembles China sourced cylindrical primary cells in Reno NV. They purchase the comments for BMS and they are assembled in China as well. They have a great 10 year warranty and the only ones not using prismatic cells in their batteries. Trojan and Relion and Rolls &#;make&#; a Lithium battery as well.
Should you upgrade to Lithium?
Contact us to discuss your requirements of 12V 150Ah Front Terminal Battery. Our experienced sales team can help you identify the options that best suit your needs.
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