Three solutions for onboard energy: who wins?

One only expects them to come down in price, because lithium batteries have incredible potential for on-board use. They are lightweight, allow more charge cycles, and for the same amount of space as a traditional model deliver more energy. They made their appearance in the nautical world in 2009, and to date only a few elite shipyards offer them as standard, others as options, and while they are commonly installed on boats that prefer electric propulsion. But how to understand the real benefits for a normal boat? Here are some elements that can help you choose and evaluate whether lithium is the right solution for you.

THE DIFFERENCES IN WEIGHT
Lithium batteries, at the same amperes, weigh less than half as much as Agm and Gel models. Everyone knows that weight in a boat is critical: it affects performance and boating comfort. In addition, the longer and more spacious the boat, the more energy it consumes, so it needs more batteries on board. Just to get an idea of how light lithium models are: a 320 Ah 12V lithium battery weighs 50 kg, the equivalent of a Gel set is 154 kg. You read that right, 110 kilograms difference, like having an extra person on board or 2 50-kilo anchors, a home refrigerator, etc. In addition to weight savings, for the same number of effective amps, there is also a smaller footprint on board: on average, it takes 3 or 4 Gel batteries (100 Ah at 12V) to get the same range as a single lithium battery. To make this comparison when comparing Gel and Lithium, we did not consider the nominal capacity of the battery, because in reality the actual capacity of the battery (indicated on the label) is never used but only a percentage. With a lithium battery (which has no memory effect) you can use up to 80% of the power reserve while with Agm or Gel you only get around 60-70%.

THE YIELD.
To talk about performance, we start with the level of “energy” that can be used without compromising the battery itself. Agm/Gel models should never be discharged to 100%, otherwise damage to the reserve and operation of the battery itself will occur. Theoretically, even Lithium ones cannot be “knocked down” to their limit, but the consequences on their efficiency are less, since they have no memory effect. This means that the efficiency remains the same even if the battery remains stationary. In addition, the Lithium one does not suffer if it is not recharged to its limit, whereas, the other models “suffer” from partial charging, with a reduction in efficiency and durability. Returning to the discussion of actual output, that is, the availability of actual amperes of the battery, we consider 80% for Lithium so, with a 320 Ah one has 250 Ah available. For Gel you have 70%, so with a 100 Ah model it is considered 70 Ah, and for Agm 60% so again on a 100 Ah model you have 60 Ah available. Therefore, the number of conventional batteries useful to achieve the same output as a single 320 Ah lithium battery varies from 4 to 6 units. A useful element in understanding the potential of lithium is charging times. “Traditional” ones must always be fully recharged, otherwise the actual available capacity is reduced due to the “memory” effect, and it takes a minimum of 6 hours for the charge to be complete. Lithium ones also charge in just one hour and do not suffer from partial charging, always providing all the stored energy.