Updated: Jul 11, 2019
Lithium battery prices have dropped in recent years, making it more affordable for the average consumer wanting to make their solar array maximally efficient. This can be done at the initial setup or after market with no major adjustments needed. Before getting started, it should be noted that our setup is lithium only and we are big fans of the efficiency it provides, along with the consistent voltage at all battery levels. Lithium is a clear winner in all categories and this article will help demonstrate how far ahead of the competition it is.
There is a stigma surrounding lithium-ion batteries and their use, expense and installation being a concern for some. They are a new technology for RVers and because of that, it takes time to come around to the immense benefits they offer at a higher up-front cost, but with a lower top-end cost. They are already in many of the products we use today such as smartphones, tablets, laptops, and vehicles like Tesla and Prius. Companies use lithium-ion batteries instead of the old school lead-acid batteries due to the lack of needing to protect against the hydrogen off gassing. This allows companies to place lithium-ion batteries in closed compartments. The technology is safer and more efficient than any other battery on the market.
The goal of this article is to make lithium-ion battery information as accessible as possible to those interested in this new technology. When we started looking at battery choices, filtering through the plethora of data was cumbersome and difficult. Most RVers were pointing toward AGM hands down, very few having had experience with lithium-ion. We were curious about lithium and did our research. As time went on, the data was clear, making the decision for us. Check out our setup here.
D.O.D. (Depth of Discharge)
LiFePO4/Li-ion (Lithium Iron Phosphate battery)
AGM (absorbed glass mat) type of lead acid battery
Ah (Amp hour) amount of DC hours of a battery (numbers range from 100 Ah to 400Ah or so)
Lithium ion batteries used in RV and vehicle use are LiFePO4, which stands for Lithium-Iron-Phosphate batteries. They are safe and stable in vehicles or RVs.
They can be stored in compartments, under beds, dinettes, seats, etc. The options are endless due to their lack of off-gasing that is a standard issue in AGM batteries.
They are most efficient at average temperatures, but can handle cold and hot temperatures.
Have a D.O.D. of 80% to 100%. Conservatively speaking they recommend 80%, but 100% isn’t an issue.
Can charge at a higher voltage of 14.4 to 14.6, which charges the battery twice as fast as AGM (like fast charging in smartphones). This is 5 times faster than AGM.
Holds a charge for up to a year without the need for trickle charging.
Voltage remains constant even with 10 times the load.
Does not require float stage.
Cycles range from 3,000 to 8,000 charges and discharges before reaching a 15-20% decline in capacity.
Average weight is around 30 lbs. for a 100 Ah battery.
Takes up less physical space than AGM
Price is around $949 per 100 Ah battery (5 times the cost of AGM).
A type of lead-acid battery using an absorbed glass mat technology to trap the gas released and recycle it.
They suffer from off-gassing needs and can be ruined if not charged at the optimal voltage.
The D.O.D. of AGM batteries is 50%.
Voltage drops as the percentage of the battery decreases. Increased load decreases voltage.
Needs an optimal float stage and optimal charge voltage.
Requires trickle charging in the off season. Doesn’t maintain a charge over time.
They have an average cycle usage of 600 before going dead, meaning they have to be replaced more often.
Average weight is around 66 lbs. for a 100 Ah battery (2 times heavier than lithium).
Takes up a lot of physical space
Price is around $189 per 200 Ah battery.
Useable Energy & Efficiency:
The D.O.D. for AGM is 50% while the Li-ion D.O.D. is 80%. This means that in optimal conditions, each can be discharged to 50% or 80% respectively. I’m using 80% for Li-ion as a conservative rule of thumb to show some deficiency in the lithium-ion product. To determine the amount of useable energy each system offers, we need to use the formula Volts x Ah x D.O.D. = kWh. We take the total voltage of the system, multiply it by the amp hours of the battery, and then by the amount the battery can be discharged. This will give a general number of how many kilowatt hours the battery will provide.
COMPARING 200 Ah Li-ion vs. 200 Ah AGM:
For the voltages to be equal across systems, we would need two AGM batteries at 12v. To make the amp hours equal, we’re going with two Li-ion batteries.
Li-ion Battery kWH (Two 100 Ah batteries):
24V x 100 Ah x 0.8 = 1.92 kWh for 200 Ah Li-ion battery
AGM Battery kWh (Two 100 Ah batteries):
24V x 100 Ah x 0.5 = 1.20 kWh for 200 Ah AGM battery
* For those fans of the dual 6V Golf Cart batteries, the numbers are even worse:
12V x 220 Ah x 0.5 = 1.32 kWh for 220 Ah Deep Cycle lead-acid golf cart battery
Here we can see that Li-ion batteries are far superior in total kWh given. If we discharge to zero on the lithium, the number jumps to 2.4 kWh! The difference is startling. You get far more power out of the Li-ion battery. To equal the same kWh of Li-ion batteries, you’re looking at needing to nearly the double the amount of AGM batteries. It's better to also go with the two 6V Golf Batteries over AGM.
Lithium-ion batteries take in energy of every voltage level, making them extremely efficient at charging. They will gladly take energy from a generator, solar, and wind at once, charging them faster and giving you more kWh. Lithium-ion can charge up in a few hours while bulk charging whereas AGM batteries can take several hours.
Weight is a major factor in choice when it comes to traveling in an RV. Making sure weight limits are not reached is a key factor in choosing which items go in an RV. Each RV has a maximum weight limit and going over it poses a threat to safety. Van and car travel have limits that are even smaller, so it becomes vital to minimize the extra weight where one can.
30 lbs. per 100 Ah battery. In the above situation, 100 Ah @ 24V of lithium-ion batteries equals 60 lbs. total.
66 lbs. per 100 Ah battery. In the above situation, 100 Ah @ 24V of AGM batteries equals 132 lbs. total.
Lithium-ion is far superior when it comes to weight management.
This one is one of the most important differences between lithium-ion and AGM batteries, simply because it effects the amount of usage you get on one charge of your batteries before needing some sort of charge from solar, portable generator, or internal generator. As stated above, the D.O.D. of lithium-ion is 80% to 100% and AGM is 50% fixed. What this really means is that you get more usage out of a lithium-ion battery for longer periods of time. In the graph below, the cycles plummet when AGM batteries are discharged under 50% making that 600-cycle AGM battery a 250-cycle battery if you try to match it to that of lithium-ion.
Example with smartphone:
Lithium-ion Discharge Capacity (Smartphone #1):
Your smartphone can be used from 100% charge to 20% or even 0% before you need to plug it in and charge it. Now, for those that have fast charging, you can plug in your fast charger and the phone will charge up to 100% four times faster than it normally takes other people to charge. You are happy.
AGM Discharge Capacity (Smartphone #2):
Your smartphone can be used from 100% charge to 50% before you need to plug it in. Unfortunately, you don’t get fast charging as an option because your phone is several years old. If you walk away for a few months, your phone is dead. If you go below 50% too often, your phone is dead for good. If you get sneaky and try to use the fast charger on your phone, you just killed your phone. You are phoneless and sad.
Which smartphone do you want?
It’s that simple as far as capacity goes, but here are some explanations that demonstrate the voltage drops as percentage of battery. What this means is that as the battery percentage drops in AGM, the voltage drops and may not power the devices you want to use. With lithium-ion, the voltage is constant, regardless of load.
Lead-Acid Voltage Plummets Under 50%
Lithium-ion Voltage Remains Constant Regardless of Capacity
This is the one that gives many people pause when it comes to switching to lithium-ion from AGM or their current setup. At five times the cost of AGM, the expense may seem overwhelming. The truth is that the cost benefit analysis is far more in favor of lithium.
Cost of batteries over 10 years using two 100 Ah LiFePO4 battery and two AGM batteries at 24V:
As you can see here, the initial cost of the lithium battery is $949 per battery, giving us $1,898, while it costs around $756 per two years, on average for a system that is equal in voltage, but 0.7 kWh less than the equivalent lithium-ion setup. The cycle difference listed above shows that you’ll need to replace the AGM batteries every year, depending on optimal usage, giving a two-year cost of $189 x 4, or $756. If you rarely use them, then you might get 5 years out of them. Regardless, you’ll need to buy multiple batteries. For the average user, you might replace AGM batteries at 2, 5, 7, and 10 years accordingly and never in 10 years for the lithium-ion battery. Lithium batteries can also last 20 years or more, which only increases the benefits of the initial cost
Cost of two Li-ion battery and two AGM batteries for 24V @ 10 Years:
Lithium = $1,898
AGM Average = $660 x 4 = $3,024
AGM Conservative = $660 x 2 = $1,512
*Lithium @ 20 years = $1,898
*AGM @ 20 years = $6,048
*This doesn’t account for the cost of gas or propane for a generator to power the AGM for hours and hours from 50% on, whereas it’ll take 1-2 hours to recharge 200 Ah of lithium-ion batteries when bulk charging.
The breakdowns above should provide a clear demonstration of the benefits of lithium-ion batteries over AGM. During our initial research into solar, we found articles extremely dense when it came to batteries and mixed opinions regarding lithium-ion. I believe for many people the cost was an initial deterrent, but upon further investigation, the numbers lean immensely in favor of lithium-ion. When accounting for constant voltage regardless of battery percentage, long cycles, fast charging, larger energy usage capabilities, lighter weight, and easier storability it becomes more and more clear that there is no other choice but lithium-ion. If you look at the average cost over 10 years of AGM, the numbers show that lithium-ion battery prices of $2000, years ago, were worth it than. It's even better at 20 years. Prices have dropped by half and are even more cost effective than before. If you want to buy locally, go with Battle Born batteries. We use them and love them. If you want to see how benficial they are for gaming, click here.
John Rushworth and his detailed blog post with the support of Vader and Boonstra. Thanks to Reinout Vader and Johannes Boonstra for the battery images and discharge charts. Check out more readings from Victron.
Special thanks to Dan Heming for his immensely helpful input and helping fix voltages and amp hours to make things more in line for comparison purposes.