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Both AGM and lithium batteries can be used for solar power systems, but which one is best, and in what circumstances?
Let’s first look at their similarities, and then we’ll look at each to see where these 2 batteries shine.
AGM vs Lithium Batteries: Similarities
Great for Off-Grid Power Systems
Both AGM (absorbent glass mat) sealed lead-acid and lithium batteries are what we call deep cycle batteries. They may look a lot like car batteries, but they’re quite different.
Deep cycle means that the batteries have the ability to be fully charged and discharged. A deep cycle battery is very useful for situations where you need a continuous source of electricity to power things like lights, computers, and household appliances.
Deep cycle batteries are great for off-grid power systems because you can discharge and recharge the batteries much more than a standard vehicle battery.
Lithium batteries are known to be maintenance-free but lead-acid batteries are not. However, AGM batteries are the exception.
Although AGM batteries are more expensive than most other kinds of lead-acid batteries, they’re maintenance-free and typically last longer than the other lead-acid batteries.
Other types of lead-acid batteries, mainly flooded lead-acid batteries, require routine maintenance of electrolytes, must always be upright in orientation to prevent electrolyte leakage, and needs a ventilated environment to diffuse gases created during cycling.
I couldn’t be bothered with trying to maintain those batteries!
Both lithium and AGM batteries are clean, safe, and you don’t have to worry about maintenance or keeping them upright. They’re worth the extra money!
Why Choose AGM Lead-Acid Batteries
The main reason most people will choose AGM batteries is that they have a lower upfront cost compared to lithium batteries.
But you can expect lithium batteries to have roughly 5 to 6 times more lifespan than AGM batteries. So lithium batteries are cheaper in the long run if you’re going to use them daily.
However, both AGM and lithium batteries will degrade naturally over time. So if you’re only going to use your battery occasionally, cheaper AGM batteries can be a good choice.
Another reason why AGM batteries are great is that they tend to handle cold, freezing weather better than other types of batteries. (Weather can affect battery performance, especially when it comes to winters.)
For more information on using lithium batteries in cold temperatures, check out my post: Do Lithium Batteries Work in Cold Weather?
Why Choose Lithium Batteries
Lithium batteries are known for their amazing cycle life. (A battery’s cycle life is the number of charges and discharges that a battery can complete before losing performance).
With a sealed lead-acid battery, you’ll have around 900 to 1200 cycles. (One battery cycle involves discharging the battery by a certain amount and then recharging it to full the amount.)
However, with a lithium battery, you can have around 5000 to 8000 cycles!
Compared to AGM batteries, lithium batteries are commonly more expensive initially but they have a better cycle life. So lithium batteries are cheaper in the long run.
Also, you can discharge a lithium battery 100%. But with a lead-acid battery, you really should only discharge it to 50% before you start negatively affecting the battery’s lifespan (although this varies depending on the battery).
So, if you can only discharge a lead-acid battery to 50%, that only gives you half of the electricity stored in the battery. Meanwhile, you’d be able to access 100% of a lithium battery’s stored electricity.
Lithium batteries are also much more efficient with electricity than lead-acid batteries.
When you put electricity inside a new sealed lead-acid battery and then you take it out, you lose about 10 to 15% of that electricity. That means you only get 85-95% of that electricity back. But when you put electricity in a lithium battery and then you take it out, you’re getting 99% of that electricity back.
Lithiums also give off electricity way easier than AGM batteries, so it’s more efficient at powering large household appliances (like your washer and dryer).
Lithium batteries are about 30% the weight and 70% the size of an AGM battery.
That’s why you’ll see things like portable power stations, meant for bringing power on your hiking and camping trips, built with lithium batteries. Consumers want to have smaller, lighter products when they’re looking to buy portable power.
A lithium battery will also out-perform an AGM battery because the voltage will stay constant, no matter how much it’s discharged. So if no matter if a lithium battery is 100% charged or 1% charged, it’ll have the same voltage.
However, the more you discharge an AGM battery, the more the voltage will drop which affects its performance.
Conclusion: AGM vs Lithium Batteries for Solar
If you don’t expect to discharge your battery more than 50% and you’re only going to use your battery occasionally (like the occasional camping trip where you don’t need much power), then the cheaper AGM batteries are definitely a good way to go.
However, in most cases, I recommend that people buy lithium batteries if they’re going to be using them every day. Lithium batteries are smaller, lighter, will last longer, perform better, and (in the long run) will be cheaper than an AGM battery if used regulary.
If you’re now wondering what kind of lithium battery you should buy, check out my post: What Is the Difference Between Lithium-Ion and Lithium Iron Phosphate Batteries?