Electrical system, Part 3 – Battery Comparison

In this table, I have compiled some different characteristics for the most common types of batteries used on board boats today. The figures are approximate as there are some variations between manufacturers. I have also created a table you can use to calculate the life cycle cost of different battery types.

Since the compilation reflects different types of batteries, I have had to round some values ​​slightly compared to what the different suppliers report. Therefore, it is possible to find suppliers who have other values than those in the table. I have tried to see the big picture to get a better understanding of the differences between types of batteries.

I also have rounded the values, so that there will be slightly clearer differences between the different types of batteries. For example, there may be suppliers of LiFePO4 that specify other values ​​for minimum DoD or charging cycles. Same thing with the self-discharge rate where I entered the highest number I found.

I have taken some liberty when it comes to defining the maximum charge and discharge currents that won’t age the battery faster than ”normal”. So take this value only as an indication of the maximum currents to give a picture of the battery type. Currently, there are no such values as Cold Cranking Amps or Continous Cranking Amps on LFP batteries. However, LFP batteries can deliver large currents and it is often the BMS that set the limits to create a safer solution with less risk of overheating or aging the batteries.

Comparison of battery characteristics
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Cost comparison of different battery types

In order to be able to compare the cost of different types of batteries, you need to compensate for the fact that different types of batteries have different amounts of usable capacity (Ah, Wh) and different lifetimes (number of charge cycles).

In this table, I have compiled information about the usable capacity and lifespan of the batteries (charge cycles).

I have also calculated equalizing (normalizing) factors so that you can compare different types of batteries even if they have different available capacities and different lifetimes.

Finally, I’ve combined the capacity and lifetime normalizing factors into a purchase cost equalization factor. With this factor, one can calculate whether one battery is more expensive or cheaper than another during a comparable lifetime.

Comparision of battery cost

To be able to compare batteries in this way, two things are assumed

  1. That one installs the same available capacity regardless of the type of battery being compared.
  2. The battery type with the shortest lifespan is successively replaced with new batteries of the same type to achieve the same lifespan as the battery with a longer lifespan.
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Example cost comparison

Suppose you want to compare the cost of a GEL battery with an LFP battery. How do you do it then?

You have already found out how much capacity is needed in the battery bank. Assume it is 24V and 400Ah

A GEL battery has 60% available capacity and an LFP has 80%. The factor to compensate for different lifetimes is 5.3 for GEL and 1 for LFP. This means that you need to replace the GEL batteries about 4 times to achieve the same lifespan as the LFP.

In the table below I have compiled data to calculate the lifetime cost of GEL compared to LFP.

GELLFP
Capacity 24V400Ah/60% = 660Ah400Ah/80% = 500Ah
Batteries6 * 12V 220Ah3 * 24V 200Ah
Purchsase cost
(inkl. VAT 25%)
4 320 EUR14 700 EUR
Lifespan cost5,3 * 4 320 = 22 896 EUR14 700 EUR

Jag har bara tittat på batterier som tillverkas av Victron.

Orsaken till att båda batterierna är från samma tillverkare, är för att få en rättvisare jämförelse. Det går att hitta billigare GEL- och LFP-batterier, men eftersom syftet med artikeln är att visa på livstidskostnader för batterierna, har jag avstått från att hitta ”billigaste” eller ”bästa” batterierna.

Victron hade inget LFP batteri som det gick att bygga en 24V batteribank med 500Ah nominell kapacitet. Istället valde jag ett batteri som ger en något större batteribank, 600Ah nominell kapacitet och 480 Ah tillgänglig kapacitet.

Detta LFP-batteri har även inbyggd BMS som kan hantera upp till 5 parallellkopplade batterier.

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I have only looked at batteries manufactured by Victron.

The reason that both batteries are from the same manufacturer is to get a fairer comparison. It is possible to find cheaper GEL and LFP batteries, but since the purpose of the article is to show the lifetime costs of the batteries, I have refrained from finding the ”cheapest” or ”best” batteries.

Victron did not have an LFP battery so it was possible to build a 24V battery bank with 500Ah nominal capacity. Instead, I chose a battery that provides a slightly larger battery bank, 600Ah nominal capacity and 480 Ah available capacity.

This LFP battery also has a built-in BMS that can handle up to 5 batteries connected in parallel.

Final words

Switching from lead-acid batteries to LFP batteries will cost more compared to changing to new compatible lead-acid batteries.

But if you want to keep the boat for several years and can afford it, invest in LFP batteries. On the one hand, you don’t have to buy new lead batteries, and on the other hand, the resale value of the boat increases.

Another indirect effect of using LFP batteries is if you use the engine or generator to charge the batteries. Because charging is faster, there will be fewer engine hours.

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