RV, Motorhome, Travel Trailer and Caravan Off-Grid Batteries
A question that is asked more and more these days, with the vast array of options available, is what I will discuss next. I will try to make it as simple as possible so that every man and his dog can be well informed to make a decision as to which is the best house battery to buy for your RV.
Here is a list of the best known and most common battery types in use in motorhomes, RVs, Travel Trailers and Caravans.
- Deep Cycle FLA (Flooded Lead Acid)
- Deep Cycle AGM (Absorbed Glass Mat)
- Deep Cycle Gel
- LiFePO4 (Lithium Polymer)
- Lead Calcium
- Lead Carbon
- Lead Crystal
Let us quickly go over the differences, pros and cons from 1 to 6 and then I will spend some time explaining the 2 most important and best batteries for off grid power.
1,2 and 3 are all Lead Acid batteries. This is the common old technology. Even thought it is called a “Deep Cycle” battery, the more it is cycled and the deeper it gets cycled, the shorter the lifespan.
What is a Cycle?
A cycle is when the battery is charged to full capacity and then being used until the battery reaches a reasonably discharged state. There are no standards to actually measure it so for the sake of keeping it simple, I will convey my own understanding of it.
Batteries have a “lower limit”. This voltage limit is the safe low voltage limit to which you can draw / use (discharge) the battery before sulfation sets in. If you let the volts drop lower than this limit, the battery will star sulfating which will significantly decrease its lifespan. Sulfated batteries can be recharged and “resurrected” in many cases but some permanent damage will remain in most cases.
So in a nutshell, a cycle is a “full” charge and “full” discharge of the battery. Many batteries have a cycle rating. If you have a battery with a 1000 cycle rating, it means that you can safely draw power from it to the lower limit and recharge it 1000 times.
The lower limit for Deep Cycle batteries are usually in the region of 50%. If you draw the battery down to 50% and charge it up to 100% every day, a 1000 cycle battery will theoretically last you 1000 days.
Deep Cycle means that the battery can be discharged to a lower level than a Starting battery. Deep Cycle batteries are made to release power at a slower rate for longer.
Starting battery vs Deep Cycle
Starting batteries are designed to give a burst of power for a short time, like when you typically start your vehicle. Starting batteries should not be drawn below 80%.
To put this in a better perspective, when a standard 12V battery in good condition is fully charged, it will settle at around 12.8V. For starting batteries, the “empty” mark is around 12.5V. It will go down to around 10V while the engine is turned by the starter, but should immediately go back up to 12.5+ when the starter is released.
On the other hand, deep cycle batteries can, in general,be discharged to around 12.2V which should be close to 50%.
Enough said about the old technology. Let us rather spend some valuable time on the newer technology.
Lithium and LiFePO4
I upgraded my own Deep Cycle Lead Acid battery bank to a LiFePO4 bank in 2010. So, since then, I have never had to look at battery water levels and no acid spills. What a pleasure. My main considerations for going the Lithium route was the Acid Spills, regular water checking and the short lifespan.
The major plus of Lithium over Lead Acid is that you can charge the battery at phenomenal rates and it has a cycle life of 30000 plus. So I calculated that this battery pack, when well looked after, can just about outlast me. Thus the difference in price was worked into the equation and seemed like a great investment.
The drawbacks of a Lithium system is that the Lithium batteries are VERY sensitive to over discharging. This means that if you let the voltage drop too low, you might loose the battery completely. The plus is that you can safely draw it down to 80% of its charge. This equates to approx 10V on the pack I own.
Because none of the equipment onboard my motorhome can run on 10V, I have a Battery Management System (BMS) to safeguard the battery pack and cuts the supply at around 11.8V.
Lithium batteries weigh around half of the Lead Acid ones for the same rating and takes around 2/3 of the space.
A BMS is a must if you go Lithium. Lithium batteries, when properly set up, is a good investment in the long run. I fitted an 800AH Lithium pack in the same cavity where from I removed a 400AH FLA pack.
Enough said, lets go to the latest greatest technology.
Lead Carbon and Lead Crystal
Lead Carbon Battery
Lead carbon is a fairly new modification to normal Lead Acid batteries which proves pretty effective. I am not going to go into the technical and scientific stuff in this post but what is most important is that Lead Carbon can be discharged 70% without sulfation kicking in. It also charges faster than standard FLA, AGM and Gel.
The drawback is that the voltage drop quite quick. Once you reach 12V, your equipment may suffer. Still way better than the standard LA options and much cheaper than Lithium. The lifespan (cycle life) is also much better due to the non-sulfating properties.
I left the best for last.
Lead Crystal Battery
Like Lead Carbon, the Lead Crystal shares the same pros with some exception. This little beast can be discharged 100%. In other words, if the battery goes DEAD FLAT, you can charge it up again without it having detrimental effects. Absolutely amazing.
The cycle life far exceeds that of AGM and Gel although it does not beat Lithium. Being a flooded lead acid battery, the weight is not much different to normal FLA batteries.
These batteries are by far the best choice currently due to the prices which are close to that of the Gel batteries. You don’t need a battery management system either. You can charge it with your standard AGM / Gel or FLA charger and it should be fine.
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