Change over to lithium batteries

Mizz Fitz came with two battery banks of lead acid batteries; both were made up of 6 volt golf cart cells.  The batteries were well used and needed to be replaced.  I opted to change them out in favour of lithium battery cells.  

Why lithium? Well they are lighter, which for my boat wasn’t a big deal; however, it is an improvement over lead acid Batteries (LABs).  There are a few reasons why I chose lithium over LABs and those reasons are widely accepted.

Lithium batteries can be discharged up to 80% of its capacity of the battery bank.  When  compared LABs where they could only be discharged to 50% of the capacity of the battery bank. 

Using my LABs as an example, I had two banks of batteries, as stated above the 6 volt golf cart batteries had a capacity of 250 amp hours, however I would need two 6 volt batteries in series to give me 12 volt @ 250 amp hours.  Note: when you put batteries in series you add the voltage.

Having 2 identical battery banks that would give me 12 volts @500 amp hours (battery bank 1 + battery bank 2 = 250 amps +250 amps =500).  Note: when batteries are put into a parallel you add the amperage.

On the surface that sounds like enough power for the boat, but don’t forget that we would only be able to use 50% of the total amp hours of the battery cells.  That means we only had 250 amp hours.

My rough guess is that Mizz Fitz would consume approximately 12.5 amps per hour; this is for refrigeration, electronics, and auto pilot, etc. Therefore, Mizz Fitz would require 12.5 amps per hour, and with a capacity of our old LABs was 250 amp hours in total we would have 20 of run time before we had to recharge the batteries.  250 amp hours / 12.5 amps =20 hours. This would mean that I would have to charge the batteries every day; not very efficient use of resources.

Let’s compare that to our new lithium batteries. I purchased 24 cells, 12 for each battery bank.  Each cell is rated at 3.4 – 3.6 volts, and 306 amp hour rated.  I put 4 groups of three in parallel giving me 918 amps, remember batteries in parallel you add the amperage. Those 4 groups were then attached in series to each other giving me 13.6 – 14.4 volts. Again remember when the batteries are in series you add the voltage.

While adding the two batter banks of 918 amp hours together that would give me over 1800 amp hours of batteries.  By the way, these batteries fit into the existing batter bank boxes with ease. That would give me 80% of 1800 is 1440 amp hours / 12.5 amps = 115 hours; that is almost 5 days.   Quite the advantage over LABs.

The other advantage is that lithium have a much faster charging rate, basically lithium will take whatever you can send it for charging current. LABs however, not so, they have an absorption rate that charges much slower. Therefore, it would take longer to charge the lead acid batteries, and thus taking more energy if using your engine to charge.  This advantage also passes over to solar panels as well. 

In conclusion, there is a significant advantage to lithium batteries, they are lighter, and I got over triple amp hour battery power in the same foot print as my LABs.  Lithium charges faster and I can use more of the amp hour rating without harming the battery cells.

The down side is cost. Lithium is more expensive initially, however, I believe over the long run you would still be a head.

If you want to know more about my installation including cost please leave a comment or contact me and I will add a post.




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