I have 8 220ah 6v golf cart batteries (Costco) for my house bank. I want to wire them such that I have a house bank of 880ah at 12v.
The historical approach is not to put too many flood batteries in one bank. If you take just one battery it has individual cells that combine to produce the desired voltage and amp hour capacity. When any charging
system looks at a battery bank it sees one battery. One cell might be dead thus lower the overall voltage of the battery as it appears. The end result is the charging
system over charges the battery and it eventually gets damaged and dies a premature death. Maybe not in a day but over time it give out sooner than it should because of your failure to notice it.
If you were to make multiple banks you could then discharge one bank at a time and recharge them as you were able and thus fully recharge them. Doing as full a recharge after a 50% discharge is the most economical way to use batteries. You get the most bang for the buck. flood batteries have the lowest absorption rate and while cheaper take more engine
power to recharge them. It's the math of operation not the cost of the batteries at CostCo.
In the end it's about managing the risk of your already spent money
. So how cheap
are you? Buying
Costco batteries on the cheap
and then trashing them won't save you any money
and cost you more if you last a long time owning a boat. If you don't last long with a boat you wasted so much money the batteries won't really count. There is the cost you buy them at but how soon is the cost to replace them? It's the bigger picture totally.
Splitting them into banks allows you the opportunity to detect a problem and switch out the bank until you find the offending battery cell gone south. Since banks should be of equal age if you replace the one battery after the initial period of maybe it was a defective battery soon it may not matter. At a 50% lifespan if one cell went bad, you really wouldn't add back just one new battery to a whole bank. It shifts the performance of the bank and suddenly the charging profile is slightly undercharging! It the other way you get hurt in the wallet.
You can lose on either end of the charging profile. Keeping flood banks of manageable size means you'll not risk the whole bunch for one failed battery.
Your best most economical approach is never buy more batteries than you need. Too many batteries always fails because you have to recharge them soon or pay the price
later. The ones sitting on the store shelf are always brand new. If you want to pinch pennies, it's the very first thing you do. Don't buy extra batteries! Buy only what you can afford and are able to fully recharge.
Not recharging fully is a pretty severe penalty. Large flood banks always recharge the last 10% dog slow. Not fully recharging 100% costs you a penalty over time. 50% discharge then 100% recharge is the sweet spot with batteries. LiFePo batteries is another story but on a budget
, they are not in sight with binoculars.
Look at it from the money point of view not the I want a big bank point of view. You can size any bank based on that approach and save money. After two weeks out the extra dead batteries are a burden not a benefit.