Why 6 volt vs 2 12 volt

[babock]

Originally Posted by CHICKDOE

in rv's we tend to focus on the long run time requirement. suppose you have true deep cycle batteries (either 6 or 12) and you run them for a while so they get a bit discharged. now it's time to recharge them and you want to use them to start the generator. or perhaps use them to power an automatic leveling system. these are high current demands. has anybody ever encountered the situation where the deep cycles just can't provide the current needed to supply these high current short term current requirements?

A true deep discharge battery like a Trojan t-105 can deliver 250A and a 12V like the Trojan T1275 can deliver around 150A before getting too much voltage drop. Pound for pound, two 6V in series will deliver the same current as 2 12V in parallel assuming same manufacturer and type of battery.

The RV Marine Batteries can deliver way more current than a true deep discharge and even these dual purpose batteries actually put out a lot of current in a boating application. Before I started using AGMs in my boat, I used these to start a 7.4L Chevy engine in a boat for over 15 years. They start having issues starting large displacement engines that also have electronic fuel injection since these dual purpose batteries have a larger internal resistance than a dedicated "starting' battery which is why most marine engine manufacturers have a minimum cold cranking amp spec which is higher than most of the dual purpose batteries can deliver. Some electronic fuel injection engines can not tolerate much voltage drop during cranking.

Bottom line, most true deep cycle batteries can put out enough current for a heavy hitting device like an inverter powering a microwave for example. The problem with flooded lead acid batteries vs AGM is that the FLA have a much higher internal resistance so you will hit the low voltage thresholds for inverters with high loads before you hit it with an AGM given the same depth of discharge of the battery.

For small current loads that most RVs run straight off 12V like levelers, heater fans, generator starter motors, etc, true deep cycle batteries have no problem.

[babock]

Originally Posted by boondocking

They also are almost 3 inches longer and weigh 27 lbs (each) heavier.

Not a really good comparison of AH capacity.

He said he couldn't find any pair of 12V golf cart batteries which of course is not true. Tons of 12V golf cart batteries in 48V golf carts.

But...if you do want to compare apples to apples...maybe apples vs more similar sized apples...

If you look at the largest 6V golf cart battery that Trojan sells which is the T-145 that weighs 72# at 260AH and compare the smallest 12V golf cart battery which is this T1260 with 140AH at 78#, you will see its basically amp hour capacity vs weight. It all scales to each other.

[Chuck_S]

I don't have the options you guys with motorhomes and 5th wheels have. Nor is there storage in the bilges for several AGM batteries.

I looked very hard so I should have written "Reserve capacity of a pair of 6v GC-type ("golf cart") batteries far exceeded any pair of 12v I could find that would fit on the tongue of my Roo, the only reason I go to this hassle." Finding battery boxes was another issue since they have to be mounted externally on my Roo.

Running a pair of Trojan T145 Plus (Group GC2H size) which have a footprint about the size of a little Group 24 battery and about 2" higher. These and a pair of LP tanks are all that will fit. So there!

-- Chuck