Question regarding dual batteries on powerboat

This is not splitting hairs, but a fundamental principle. Instead of personal attacks why don't you post relevant data? For example, what is the minimum acceptable voltage to discharge a battery of different types.

 

I did. From the very start. Gonzo, I don't have any time for this endless discussions just to feed your ego.

 

Too much tete ta tete!

The discharge of a deep cell battery is slower.

The amount of discharge impacts the life of the battery. Deeply discharging them can ruin them. It is easy to see Gonzo's confusion about the way it was worded. He doesn't want the OP to think they can run them down all the time!

Most of the time, many boat devices won't function under certain voltage minimums. I believe the Furuno mfds have 11.5v cutouts. Many dc systems are engineered to drop devices or stop distribution below 12v. Obviously, rx doesn't mean running the voltage to zero!

If a good contributing forum member says something a bit incorrect, just clarify it, don't quote them. Quoting them is not necessary unless you desire the tete ta tete, which is not always a benefit. If you clarify something for them, it is more edifying than quoting them and pointing out they are wrong. Save that for times when you are uncertain and want their reply!

<signed>

Dad

 

Furuno equipment with 12-24 V nominal will work from 11 to 28 V. Modern electronics are less sensitive to voltage fluctuations. Ignition systems will start at 10V.
In general, battery ratings are calculated from fully charged to 10.5V. However, to compare available energy (capacity) from batteries, it is necessary to use Peukert's equation. The exponent on it is obtained by experimental results. It provides an approximation of capacity at different C rates. The formula models the discharge curves, which normally shows that capacity diminishes at higher C rates. The reason for it is that it takes time for the chemical reaction to diffuse through the plates, so there is a lag. Because of the lag, starting batteries have more plates that thinner.

 

I recently bought 3 batteries for the boat.
An AZ marine starting bat for $99 for starting
Duralast 27DP-DL Group 27 Starting Marine and RV Battery (autozone.com)

Two 6 volt GC15 Deka bats from Lowes for the house

The 2 Golf Cart batts easily start the v8 engines.
Deka 6-Volt 448-Amp Golf Cart Battery in the Power Equipment Batteries department at Lowes.com

If your getting FLA batteries, at least make sure you can add distilled water to the cells when needed. Some you can't, they just want you to get a new battery than add water, theory being that once it has used up the water, the battery is likely shot. I will say that for automotive batteries, I have never been able to fix them by adding water, adding water was just a waste of time. Most either were sulphated or developed a shorted cell.
Batteries just dont last as long as I wish. I think if you got 10 years from one, that would be great. That has only happened twice for me in 50 years remembrance.