Only one battery?

[Richie]

Thanks guys for the feed back. Yes, it only has one coach battery. It does have a tray for 2 batteries. I checked on 2 6 volt batteries but a 6 volt battery weighs 64 lbs. each. The tray doesn't look like it could handle 2 of those heavy mama's.

[Winemaker2]

Originally Posted by Richie

Thanks guys for the feed back. Yes, it only has one coach battery. It does have a tray for 2 batteries. I checked on 2 6 volt batteries but a 6 volt battery weighs 64 lbs. each. The tray doesn't look like it could handle 2 of those heavy mama's.

Reinforce the tray and go w 2- GCs
Most economical AHs you can buy.

[Winemaker2]

Originally Posted by Capt Steve

"You can draw a deep cycle battery down to 20% capacity, meaning you can use 80% of it without " damaging " it."

That is not true unless you consider seriously shortening the batteries life as not "damaging it". Nothing worse for a battery than to overdraw it down. At less than 50% of capacity, the voltage will be so low as to approach useless and you will be damaging anything that is voltage sensitive if it even works at all.

I used to agree w/ you and disagree w/ Twinboat - I now have a very different perspective after looking at several cycle life curves and running some calcs.
My new perspective...

If you look at a typical Life Cycle curve you in fact see what appears to be a sharp decline in life with increasing DOD.
There is no precipitous drop at or below 50% DOD - if it damaged the batty you should see an inflexion in the curve at 50%
Run some rough calcs on how many cum amps you can get from and batty / bank...
So assume for simplicity a 200 AH bank - fairly typical of a 2-6V GC FLA bank-
Pick a few points on the life cycle curve - say as follows

30% DOD delivers 60A over 2050 cycles or a total of 123,000 A
at 50% you get 100 A over 1150 cycles or a total of 115,000 A
at 80% you get 160 A over 675 cycles for a total of 108,00 A

So if you consider the 15,000 total A - roughly 12% reduction - to be "destroying" you battery you are correct - I no longer see it that way.
and the 12% reduction is from 80% DOD vs 30% - if you look at 80% vs 50% it is only 7,000 A or a 6% reduction in life cycle capacity.
There is more to batty life than how many years folks report theirs lasting - you need to consider how much power it delivers and few if any keep track of that kind of data (I have seen one member on another forum with a monitoring system track & report Life Cycle Amps Delivered - the rare exception)

I am surprised that they carry the life cycle curve all the way to 100% DOD as I DO agree and read in several publications that running a batty completely flat causes irreversible damage

What am I missing or error in the logic or calcs???
Thanks to Twinboat for opening my mind - you have made a believer

[twinboat]

Originally Posted by Capt Steve

"You can draw a deep cycle battery down to 20% capacity, meaning you can use 80% of it without " damaging " it."

That is not true unless you consider seriously shortening the batteries life as not "damaging it". Nothing worse for a battery than to overdraw it down. At less than 50% of capacity, the voltage will be so low as to approach useless and you will be damaging anything that is voltage sensitive if it even works at all.

6 of one, 1/2 dozen of the other.

Run one down in 500 cycles or run 2 down in 1000 cycles. In either case your buying 2 batteries in 1000 cycles.
There is a whole lot more to it, and 2, or more, batteries will give you more capacity depending in how fast you draw it down. The charts list the typical 20AH specs, but at the 10 or even 5 AH specs the battery has less capacity.

In my case, I don't have room for more capacity. The price I pay is replacing the batteries sooner then if I had double the capacity.

11.5 volts is 10% lower then 12.6 volts. What 12 volt items can't handle that ?

[Mark_K5LXP]

The numbers don't lie and there's a few intangibles beyond just Ah vs cycles.

An important factor to consider is the end application. If you're full time and you're cycling your batteries down to 20% SOC daily, then you might want to bump up the capacity a bit both for runtime margin and maybe a bit better longevity. But for the vast number of users out there that maybe take a few trips a year or just go on weekends, you're not buying anything by limiting to 50%. Your batteries will crap out due to age or damage long before cycle life is hit. I consider it false economy to buy a set of batteries then only use half - you're paying twice as much for what you're using and odds are you'll end up taking the cycle life you paid for and painstakingly saved to the recycler,

In my experience it's better to burn out than fade away. I would rather hit the cycle life limit and know I got my money's worth and get a new set, rather than suffer through limping an old battery along after it has passed it's calendar prime. Especially in RV's that can sit for months at a time the opportunity for a battery to become wounded through neglect is pretty good, so what's the point in babying it only to have it suffer damage during storage or compromised charging over the course of years. Use 'em hard, charge 'em regular and if you're lucky you'll use them up before they give up.

Mark B.
Albuquerque, NM

[Hey Vern]

There is nothing like having enough battery capacity. In my Stealth Toy Hauler, I have room for 2 group 24 deep cycle batteries on the factory mounted space behind propane tanks, Then I found a space in the storage pass through to hold 3 more group 24's. At 85 Amp hour each, that gives me 425 amp hours. That will give me about 5-7 days without recharge. You can always find room for additional batteries somewhere.

[Ron Dittmer]

Originally Posted by Winemaker2

Reinforce the tray and go w 2- GCs
Most economical AHs you can buy.

Our rig came with two 12V batteries in a slide out tray. To gain the extra height for 6Vs, I had to ditch the tray. I installed a steel bottom and manually slid in two 6V AGM batteries from Sam's Club. Being zero maintenance, the tray is not missed. That was 3.5 years, 4 RVing seasons ago. The two batteries remain in great condition, offering full capacity performance. It was one of my best mods with our rig. You can read about the details with pictures HERE.

Here is what we originally had with two 12V batteries in a slide out tray.
I went through 2 sets of these, getting only 2 good years from each set.


This is today without the tray, two 6V AGM batteries.
Being AGM, there is never a boil over and nothing to maintain except their charge.
4 RV seasons so far and these hold a full charge to this day.

[paddykern]

MB Sprinter B+/C- only came with one 12VDC automotive battery.
Marginal if using furnace and not a true deep cycle battery.
Replaced with two 6VDC AGM true deep cycle golf cart batteries.
Required a custom battery tray to achieve this.
More capacity, true deep cycle.
Still have not had a chance to see what the difference is but should be much better.

[hamfam]

My family owns a 31 ft Class C gasser. It only has one 12V house battery. I replaced it last year with a RV/Marine Deep Cycle battery. I could have gone with two 6V batteries, but decided to leave it. We boondock most of the time for 2-4 days. Never had any issues with the battery, just run the genny a bit in the morning and at night while making coffee, watching TV etc. Good Luck and Happy Holidays!

[Teamfoxy]

Originally Posted by twinboat

6 of one, 1/2 dozen of the other.

Run one down in 500 cycles or run 2 down in 1000 cycles. In either case your buying 2 batteries in 1000 cycles.
There is a whole lot more to it, and 2, or more, batteries will give you more capacity depending in how fast you draw it down. The charts list the typical 20AH specs, but at the 10 or even 5 AH specs the battery has less capacity.

In my case, I don't have room for more capacity. The price I pay is replacing the batteries sooner then if I had double the capacity.

11.5 volts is 10% lower then 12.6 volts. What 12 volt items can't handle that ?

One should remember that the voltage at any light or appliance will always be lower than at the battery. In any DC circuit, there is some voltage drop in the wiring between the battery and the light or appliance. The larger the wire diameter (smaller gauge) the less voltage drop you will have. There are calculations to determine the size wire needed based on how long the wiring run is and the allowable voltage drop. Lights are allowed to have a 10% voltage drop, but any motors are only allowed a 3% drop. Running a motor at low voltage causes it to overheat.

[Mr_D]

Originally Posted by twinboat

A single 225 AH, 12 volt battery would be huge, about the size of 2, 6 volt GC2 batteries.

You may have mixed up RC, ( reserve capacity ) with AHs.

A LifeLine 8D 12 v battery is the size of two 6v deepcycle batteries and weigh 160#'s each. They have 255 amp hours at the 20 amp discharge rate. Cost almost $700 each.

[Mr_D]

Originally Posted by twinboat

6 of one, 1/2 dozen of the other.

Run one down in 500 cycles or run 2 down in 1000 cycles. In either case your buying 2 batteries in 1000 cycles.
There is a whole lot more to it, and 2, or more, batteries will give you more capacity depending in how fast you draw it down. The charts list the typical 20AH specs, but at the 10 or even 5 AH specs the battery has less capacity.

In my case, I don't have room for more capacity. The price I pay is replacing the batteries sooner then if I had double the capacity.

11.5 volts is 10% lower then 12.6 volts. What 12 volt items can't handle that ?

12 v batteries are considered fully charged at 12.7 volts and totally dead at 11.9 - 12.0 volts according to the chart I just looked up. 12.2 is approx half gone and is when recharging is recommended for max life.

[Persistent]

The 50% draw rule of thumb has little to do with service life.
Example:
100 ah battery
80 % draw down cycle life 300 X 80 = 24000
40% draw down cycle life 600 X 40 = 24000
Same amp/hrs per life.
See battery mfg's published data for any individual battery.

[twinboat]

Originally Posted by Mr_D

12 v batteries are considered fully charged at 12.7 volts and totally dead at 11.9 - 12.0 volts according to the chart I just looked up. 12.2 is approx half gone and is when recharging is recommended for max life.

Time for some modern charts.