I read the Colin Haines letter (PBO June 2018) with interest. It seems to me the root cause of his problematic battery bank is spelled out in the letter.
He says: ‘My battery bank is rated at 305Ah capacity and the individual ages of the batteries vary between 7 and nine years old’.
It is the different age of the individual batteries that is the cause of the problem.
When you create a domestic battery bank by wiring batteries in parallel it is vital that the batteries are as exactly the same as they possibly can be. You are, in effect, creating one big battery and if the batteries are in any way different then some of them will overcharge and others under charge.
Batteries age and over time they become electrically different from a new one.
When creating a domestic bank all of the batteries need to be the same make, type, rating and age. Ideally they should be from the same production batch.
It’s a good idea to fully charge each of the new batteries individually before creating the bank.
The link cables between them should all be of the same length and you should only ever connect to the positive at one end of the bank and the negative at the other end of the bank. Do the job properly, paying careful attention to connections, and protect them from corrosion.
Do it right and your investment will be rewarded by reliability and longevity. Ian Loffhagen Rowlands Marine Electronics