One of our principals used AGM batteries for over 20 years in his cruising sailboat, covering thousands of miles.  But after regularly changing these batteries out every two or three years, he decided in 2013 to give lithium batteries a try.  He obtained samples directly from China, tested them, and found a quality manufacturer that was above the rest.  After thousands of ocean miles with that original battery bank that is still going strong, we can attest that Lithium is definitely cheaper.  Seriously cheaper!

To compare the two options, AGM vs. Lithium, you need to consider not only the up-front cost but the full lifecycle cost.  And the best way to do that comparison is to look at the one-time up-front Lithium cost, and compare that to the several times you’ll have to replace your AGM’s to equal the life-time of the Lithium batteries.  We know that up-front Lithium cost is a big ticket, but we have some suggestions on how to soften that based on the payback you are receiving in avoided AGM replacements.

Let’s start by looking at that Lithium costs.  Suppose you currently have a 210 Ah useable AGM battery bank in your boat, RV or solar bank (rated 420Ah).  That bank consists of (2) Deep Cycle 8D AGMs, that cost $940 each, or $1,880 total– but recognize that only 210Ah is useable, as regular use below 50% seriously degrades the life your AGM’s - let’s call that OPTION A.  Or perhaps you have lower quality AGM deep cycle, called “Brand X” that is 200Ah and costs $370 each, or $740 total – let’s call that Option B.

On the Lithium side let’s say you use the Blue Heron Drop-In 210Ah Lithium as your replacement battery, at a cost of $1,299 each.  Note that the single Blue Heron Drop-In of 210Ah has 210AH that are useable without damaging the battery –  we’ll call that Option C. 

In summary, up-front cost is:

OPTION A – quality AGM’s of 420Ah total, (2) AGM’s at $1,880 total

OPTION B – cheap AGM’s of 400Ah total, (2) AGM’s at $740 total

OPTION C – Blue Heron 210Ah battery, 1 battery at $1,299 total

So we know AGM’s don’t last as long as Lithium batteries, but how do we compare them cost wise?  The easiest approach is to look at life-time costs.  If we assume you do all the work yourself on replacing the AGM’s, the following lifecycle costs apply.  If you pay someone to do that work, then the life-time costs are even higher for the AGM option.  It is a ‘no-brainer’ just considering the battery costs.

Our Drop-In batteries are rated at 6,000 cycles, while high quality AGMs are rated at 550 cycles, and cheap AGMs at 350 cycles.  That means over the life of your Lithium battery you would have had to replace your quality AGM’s 11 times, and your cheap AGM’s 20 times over.

Life-Cycle Costs;

OPTION A - = $1,880 X 11, or                                                    $20,680               (Quality AGMs)

OPTION B - = $740 X 20, or                                                       $14,800               (Cheap AGMs)

OPTION C - = $ 1,299, or                                                            $ 1,299                (Blue Heron lithium)              

Okay – we know you may not keep your RV or boat long-enough for those lithium batteries to reach end of life, and then realize the above savings.  But, let’s look at it another way.  Let’s look at the breakeven point of Lithium purchased outright up front, vs. quality AGM.  Let’s just assume your quality AGM’s last a full three years.  That means you are spending ($1,880/36 mos.) or $52 per month for your AGM option.  So, in ($1,299/52) months, or 25 months, your AGM monthly budget would have equaled the cost of the lithium battery bank.  So, 25 months is your breakeven point.  After 25 months you are coming out ahead with your lithium battery bank.  That’s all it takes!

And there are other intangibles when going with Lithium, shorter charging times, lighter weight, more space available, less maintenance, helping on resale value of your boat or RV, and avoiding the hassle of the surprise early demise of your AGM battery bank, and the cancellation of cruising or travel plans.  Or being stuck in some out of the way place where you have to pay 3X to replace your AGM batteries.  So, you could say … “Priceless!”

(This technical article is the property of Blue Heron Battery LLC and may not be copied or reprinted in whole or in part without the express permission of Blue Heron Battery LLC.)