A LiFePO4 battery is the best RV deep cycle battery you can get today. For more than a century flooded led-acid batteries have been tried and true workhorses. In the past they were the kind of deep cycle batteries used in RVs. But they had many shortcomings four of them being that they were very inefficient, they were only good for two or three hundred cycles if you used 50 percent of their capacity, they were slow to charge and if you discharged them below 50 percent they would be damaged greatly shortening their life.
A common misconception is that deep cycle batteries can be completely discharged. I have even heard several salesmen tell people this. I don't think they were trying to mislead them, they just new nothing about deep cycle batteries. Most of the people I talk to have this idea and didn't know you can't discharge a Lead-acid deep cycle battery 100 percent. Even most battery labels don't state that you can't. They don't say you can in black and white either, but, they usually state the attractive capacity which leads anyone who doesn't know about batteries to think they can use all of that attractive capacity.
Now there's a better option for RV deep cycle batteries that can be discharged to 100 percent time after time. Technically you don't actually discharge them to 100 percent, but you get to use 100 percent of the capacity you paid for, and most of it is above 12 volts.
Today there's a new kid on the block, LiFePO4 batteries also known as Lithium Iron Phosphate batteries. These are the very best deep cycle batteries for an RV. LiFePO4 batteries are serious workhorses and they don't have the shortcomings lead-acid batteries have. LiFePO4 batteries are lighter than led-acid batteries, give off no gasses, so no venting is required, provide tremendous capacity, can be discharged to 100 percent of their rated capacity and require no maintenance other than occasionally checking cables to be sure they're tight.
LiFePO4 batteries last thousands of cycles, are 99 percent efficient, can be charged fast, have a flat discharge curve so they will stay above 12V for 90 percent or more of their discharge cycle regardless of whether you draw one amp or the full rated capacity of the battery and they are extremely efficient during both the charge and discharge cycle just to mention a few of their advantages.
Their efficient charging is a real advantage to anyone using solar because unlike lead-acid batteries, Lithium Iron Phosphate batteries take 99 percent of the power you put in them and they take their max charge current until they're almost full.
The best part is you get all that power back when you discharge them. These are awesome batteries capable of outworking, outperforming and outlasting the very best top of the line lead-acid battery made today. There are several LiFePO4 batteries on the market. Some of the best are made by Rebel Batteries. I have used several of them, and a couple in extreme tests and haven't had any failures.
For those who don't know a deep cycle battery is different from the battery in your car. An automotive battery is designed to provide a high current for only a few seconds. A deep cycle battery is made to provide a constant current for a long period of time. Using a car battery as a deep cycle battery will destroy it in only a few cycles.
What size deep cycle battery do I need?
What size battery you need will depend on what you plan to power with it. If all you want to power is a few lights, maybe a small 12 volt TV and a fan overnight, a reBel Batteries 50AH battery would easily cover you.
If you plan to power a little more like a water pump and a refrigerator overnight you should move up to a reBel 100AH battery.
If you're going to camp for more than one day I would go with more than one battery or maybe one large two or three hundred AH reBel LiFePO4 battery.
If you will be powering large loads like an air conditioner, heater, microwave oven or any appliance that requires several hundred watts at the very least you will need two hundred amp hours of capacity or more. How much more will depend on your individual need for power. For more information on reBel batteries and more articles on Lithium Iron Phosphate batteries see this page.