Battery Talk: Flooded Acid vs Lithium LiFePO4

Today we’ll be discussing deep cycle flooded acid batteries compared to Lithium LiFePO4. Flooded batteries have been around for a very long time and most of our customers are familiar with them, whereas Lithium LiFePO4 chemistry is still relatively new. LiFePO4 refers to the battery chemistry, which stands for Lithium, Iron, and Phosphate, which we’ll refer to now simply as LiFePO4.

When it comes to off-grid energy storage, deep cycle flooded acid batteries remain the most cost effective & reliable solution for the majority of off-grid applications. Before explaining why, you should know I’m really unbiased... The Cabin Depot™ offers LiFePO4, flooded acid, and sealed/AGM for any off-grid application in a variety of sizes from many different manufacturers. We’d prefer you choose the right battery, properly sized for your system - not just the cheapest because you think you’re saving money, or the most expensive model on the shelf because the internet said it was the best.

There is certainly a place for LiFePO4 batteries depending on the application, and they do have some performance advantages, but the single largest disadvantage is cost which is undeniable. LiFePO4 batteries are very expensive, and the cost difference is substantial. There will of course be those who disagree with my opinion, beginning their pro-LiFePO4 arguments by referencing their own experience with flooded batteries that have failed prematurely (often due to their own neglect) and quoting internet sources & specs (primarily from biased LiFePO4 resellers & manufacturers). The cost vs payback scenarios are usually inaccurate, overinflating the cost & downplaying the performance of flooded batteries to make the math work in favour of LiFePO4, effectively comparing apples to oranges… 

We’ve all been programmed by skilled marketers to think that because something is more expensive, it must therefore be better. That’s simply not true. When sizing an off-grid power system, the correct battery type & size should be based on:

• The electrical loads you want to service: is this a back woods cabin with limited electrical loads, an RV or Boat with smaller 12v devices to power, or an off-grid home with all the modern amenities?
• The type of system you will have: is this a seasonal/weekend retreat, or full time year-round?
• Your desired autonomy: how many hours or days do you want to rely on battery power alone if you have no sun, wind, or generator to recharge?
• Most importantly - your budget!

Using this as a crude example relating specifically to cost:

• A “cheap” 100Ah 12v LiFePO4 battery will cost between $500 and $800. These “cheap” batteries often carry few safety certifications and lack long term testing in real-world environments. I’m also skeptical of their true capacity and advertised cycle life, as the companies selling them exist primarily online and have only been around a couple of years. More established and reputable companies offering quality brand name 100Ah 12v LiFePO4 batteries will cost $900 to $1600 on average. 
• You can pick up a “cheap” 100Ah 12v flooded acid battery for around $100 to $130, the main difference being that they have been tested and certified. Quality brand name 100Ah 12v flooded batteries will range from $150 to $250. Comparing apples to apples on usable Ah (or Wh), you’d have to buy 2x deep cycle 100Ah batteries assuming a 50% DOD. You’d walk away with the same or more capacity as the LiFePO4 would offer, but with money left in your pocket.

Operational Advantages & Disadvantages

Claimed higher cycle life, the ability to cycle down to below 10% DOD, low maintenance, lightweight, and the ability to be stored below 100% SOC for long periods of time without damage are the most commonly promoted advantages of lithium LiFePO4 chemistry. But what’s rarely discussed is that LiFePO4 batteries have limited operational capacity in cold climates. Most no longer accept a charge at -4C (25F) and shut down completely at -20C (-4F). This may not matter for a full-time occupied heated off-grid home, but for cabins that aren’t occupied & heated full time in winter, temperature is very important. By comparison, a flooded battery will not freeze if charged, and although the capacity is lower it will still operate at sub-zero temperatures well after its LiFePO4 counterpart has shut down. If you have a problem with your charging system, there’s no easy way to diagnose what’s wrong with a LiFePO4 battery. But with a flooded battery, you can test the electrolyte specific gravity (SG) using an inexpensive hydrometer or refractometer. That test will tell you immediately if you have a problem with a particular cell, if the battery charge is equalized, or if you may have stratification or plate sulfation. Having this ability to check the battery condition is very important and often overlooked when customers are starting out with their first off-grid system. Is it as convenient as hooking up a LiFePO4 battery and walking away? No. There’s a little bit of work involved such as checking & topping up electrolyte levels on occasion. But you can buy more flooded batteries & have the same or higher usable capacity for less $. It’s that simple.

Despite the huge marketing efforts being put into promoting LiFePO4 batteries, the vast majority of off-grid battery sales remain flooded acid. I know many living off-grid with modest systems who have been using Trojan T-105 or Rolls L16 batteries for more than 10 years successfully. Surette have announced new Rolls flooded battery technology now that promotes a higher cycle life and lifespans of 14+ years. Flooded batteries in their current form have been used for over a century and their technology continues to evolve. LiFePO4 used in off-grid applications is still only a few years old by comparison. I’d suggest that if one could afford the up-front cost of LiFePO4 and sized their system correctly, adhering to temperature limitations, with regular daily loads to service, they are a good option to consider. But each situation is different. And at the same time, if someone has a seasonal or weekend use off-grid solar powered cabin, knowing they can achieve 10 years of performance from a flooded acid battery bank if properly maintained, I’d be hard pressed to recommend LiFePO4. Especially knowing that 5 or 10 years from today, energy storage solutions and battery chemistries will continue to evolve with potentially lower cost alternatives coming to market.

-Gord