[Architeuthis]

Having replaced battery banks with hundreds of batteries we looked into these questions and our basic conclusion was that the best is buying single cell batteries of the ampacity required.

Cells fail. A single cell failing will sometimes take out the bank as they can fail explosively. These failures are the result of an open circuit and are not as common as a short circuit. A single cell short circuit means the bank will continue to function at a lower voltage.

Sometimes for practical or cost reasons you do not want to use that configuration. For example when a single cell becomes so heavy it cannot be handled safely then it is better to go with smaller cells in parallel and series to get the voltage and ampacity required.

When it comes to sailboats the best option, individual cells, may not be possible due to how the boat is made. That means that practical considerations will outweigh what is best for the batteries.

For most modern well equipped boats the idea battery bank size would take up the whole boat. So we use a variety of compromises and charging systems to offset that.

The result is those who are giving exact answers are…well exact answers are what people like so they are doing what people like but those banks are not going to last the 15 plus years that I have seen in well designed banks.

Battery bank life is one of the costs of banks on boats. Reliability is another.

General rule would be to fit as many batteries as you can fit, or want to buy, or want to lug around. Then break them up into banks to get increased reliability and the ability to mix banks of different ages and capacities. Then plan to replace them depending on condition which will vary depending on many things, which includes use.