Stumpalump said:
There are two types of marine batteries. Marine cranking batteries and deep cycle. The dual use is a marine cranking battery.
... and respectfully .... you would be quite wrong sir.
FWIW this info below comes from my boating friend, a PhD chemist and physicist, who makes batteries for US Navy torpedoes. Luckily ... he gives me his old 12V batteries they used for bench testing! Gotta spend that budget every year, you know!
WALI4VR said:
What exactly is different between deep cycle, cranking and dual- purpose batteries. Seems to me dual let u have your cake and eat it too!
CRANKING - Plates/design optimize high load cranking amps, i.e., the peak cranking amps on a V6 OB starter is ~250-amps, dropping to < 200 whilst continuing to crank.
Purpose - Designed to discharge a large amount of energy for a short period, not designed to be deeply discharged.
When such a cranking battery is deeply discharged, it can suffer damage that affects its useful life and capability to charge back to full capacity.
DEEP CYCLE - Typically used for static loads over a long time.
Purpose - Designed to discharge a small amount of energy over a long period, often until most of the battery’s capacity has been fully discharged.
Deep cycles are built to discharge up to 75% of their capacity without suffering any damage. The 'safe' amount of discharge varies depending on who built it — some are designed only for a 45% discharge, while others can discharge 75% or more of their total energy capacity without any negative effects on long-term performance.
Look at the difference between them by comparing a track&field sprinter vs. a marathon runner. A cranking or 'starting' battery performs like the sprinter, i.e., delivering lots of power before running out of breath. Whereas the deep cycle battery is akin to a marathon runner, offering far less speed, but for much greater endurance, i.e., time.
DUAL PURPOSE - A blend of both, a cranking/starting battery made with heavier plates, and designed to withstand a deep discharge.
Purpose - Designed for nominal cranking duties and minimal discharge use, sort of a blended use, if you will.
Example, I would never use a dual purpose one to start a 300hp V8 OB motor, or inboard motor, nor would I personally run a 12V trolling motor on one. But I have used them on numerous dual or triple battery boats where we'll crank the V6 OBs with them, then run our electronics off the same battery whilst on anchor or drifting, i.e., motors off.
IMHO the best value, and my friend concludes this too, for 'general use' is a marine battery sold by Walmart. They are fresh, carry the month of manufacture on them and they are made by Johnson Controls, the same company that owns and sells Optima gel-type batteries.
To me it is prudent that a boater understand that they are really 3 distinct battery designs and applications.
TIP - For those running dual battery installs without an electric trolling motor, two dual purpose ones are awesome! But never run a 1-Both-2-Off battery switch on both, as they will equalize if/when you shut off the motor. What I do is use battery #1 on odd days of the week and #2 on even days of the week. Yes, you may have to check your iphone's calendar :roll: .
Or, if you have long runs to your favorite fishing hole ... run out on #1 and back in on #2. Use cycles like this help equalize use, load and charging!