If you're buying a new battery for your boat, you'll usually have three broad categories to consider:
- Traditional lead-acid
- Absorbed glass mat (AGM)
- Lithium iron phosphate (LiFePO4)
These batteries exist on a spectrum, with lead-acid batteries being the most affordable, most difficult to maintain, and shortest lasting. At the other end of the spectrum, lithium batteries are by far the most expensive and long-lasting option. That leaves AGM batteries in the middle position, but are these batteries a genuine "sweet spot" for price/performance, and do they make sense for your boat?
AGM vs. Lead-Acid: More Similar Than You Think
While lithium batteries use fundamentally different chemistry, AGM and traditional lead-acid batteries use the same underlying reaction. In other words, these two technologies have more commonalities than differences. The primary difference comes from their internal arrangement, and that's why AGM batteries can offer less maintenance and longer life.
You may sometimes hear traditional lead-acid batteries referred to as flooded lead-acid batteries. Internally, these batteries use a lead anode flooded in an acidic electrolyte solution. The heating of the electrolyte causes the water to heat up and evaporate, so flooded lead-acid batteries require water top-ups as maintenance. Flooded batteries can also spill in extreme circumstances.
AGM batteries use the same internal chemistry but utilize fiberglass mats to wick the electrolyte solution. As a result, these batteries are "dry" and sealed. You don't need to add water to an AGM battery, and it cannot spill. The internal design and lack of maintenance also mean these batteries typically last longer than flooded lead-acid batteries.
Selecting the Best Battery for Your Boat
Flooded lead-acid, AGM, and lithium batteries are all viable options for most marine applications. Choosing the best battery for your boat depends on your needs and priorities. However, AGM batteries offer numerous advantages, making them a solid choice as a price/performance sweet spot. In particular, they can last up to several years longer than equivalent flooded batteries.
If your primary goal is to buy the most affordable battery available, flooded lead-acid batteries are still the best choice. These cheaper batteries can be particularly cost-effective in larger banks. On the other hand, LiFePO4 batteries can last for four times as many cycles as AGM batteries. This huge lifespan makes them a great choice for longevity, but their high cost can be painful on your wallet.
Ultimately, that makes AGM batteries a good choice for boat owners willing to spend a little more money for a longer lifespan without the extremely high cost of converting to lithium. Additional benefits, such as their no-spill sealed design and lack of maintenance requirements, help to give AGM batteries an excellent balance between cost and performance.
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