6 VOLT BATTERIES, MINIMUM VOLTAGE

[LVJJJ]

I used to know this but don't remember much anymore.

I'm using two 6 volt golf cart type batteries in my 2005 Trail Cruiser. How low can I let the batteries run down? Right now I'm testing how long they will run the furnace in anticipation of several days boondocking. I run the furnace all the time adjusting it for day and night.

After 4 days the voltage is 11.3 while the furnace is running but jumps back up to 11.8 when it stops. Am I ruining the batteries at 11.3?

[ktmrfs]

Boon Docker wrote:

ktmrfs wrote:

Boon Docker wrote:
Yes, you are killing your batteries.
11.8 is 30% SOC
Should never let the batteries get below 12.1 (50% SOC)

big misconception on never going below 50%SOC. A good rule of thumb for 12V RV/marine but not for a GC2 true deep discharge battery.

Many many many GC2 batteries are speced for hundreds of charge discharge cycles down to 25% SOC. IIRC the common garden variety Trojan T105 is spec'd for 500 charge discharge cycles down to 25% SOC, and they define end of life at something near 75% of spec'd new capacity.

Totally Wrong

Quote from Trojan web site regarding GC2 6v batteries.

Shallow discharges will result in a longer battery life.
50% (or less) discharges are recommended.
Do not fully discharge flooded batteries (80% or more). This will damage (or kill) the battery.

Yes 50% will give you fantastic cycle life, but you can go much deeper and still have long life.

And without knowing application specifics, I can understand why Trojan gives a "rule of thumb" of 50%. Now if I was doing a deep discharge every day, 50% would be a good compromise between life and battery capacity.

If I only use the batterys for 30 or so days of dry camping/year, I'd not worry at all about going to 75%, I'd still get close to 10 years of life out of the batteries if I maintained them well.

And I'd never fret about "what do I need to turn off, we are at 50% and outside of generator run hours" it would be well, I'll watch but not worry.

Look at the trojan cycle life chart for various Trojan Deep discharge batteries

https://pbase.com/mainecruising/image/164698591

true, 50% gives longer cycle life and if you really need huge cycle life stay in the 50% or less. But even the venerable std t105 gives 700 ish cycles at 75% DOD and yes 50% DOD gives well over 1000.
how many RV'rs will ever need 1000+ cycles of deep discharge.

Now look at the 12V deep discharge line, yup those don't want to go below 50%, and at 50% are well below in cycle life compared to the GC2. and at 75% cycle life is in the few hundred.

I agree, going below 80% is BAD

And as mentioned I've run multiple sets of Trojan GC2's down to 25% hundreds of times w/o any noticeable loss of life, consistent with the data on the graphs.

[time2roll]

11.3 is on the low side of low. Now the important thing is to get them up to 14.8 and hold for two hours. Then go again.

The furnace should keep running down into the 9 volt range in an emergency but that is too low to get long life from the pair of GC2.

[Boon_Docker]

ktmrfs wrote:

Boon Docker wrote:
Yes, you are killing your batteries.
11.8 is 30% SOC
Should never let the batteries get below 12.1 (50% SOC)

big misconception on never going below 50%SOC. A good rule of thumb for 12V RV/marine but not for a GC2 true deep discharge battery.

Many many many GC2 batteries are speced for hundreds of charge discharge cycles down to 25% SOC. IIRC the common garden variety Trojan T105 is spec'd for 500 charge discharge cycles down to 25% SOC, and they define end of life at something near 75% of spec'd new capacity.

Totally Wrong

Quote from Trojan web site regarding GC2 6v batteries.

Shallow discharges will result in a longer battery life.
50% (or less) discharges are recommended.
Do not fully discharge flooded batteries (80% or more). This will damage (or kill) the battery.

[ktmrfs]

Boon Docker wrote:
Yes, you are killing your batteries.
11.8 is 30% SOC
Should never let the batteries get below 12.1 (50% SOC)

big misconception on never going below 50%SOC. A good rule of thumb for 12V RV/marine but not for a GC2 true deep discharge battery.

Many many many GC2 batteries are speced for hundreds of charge discharge cycles down to 25% SOC. IIRC the common garden variety Trojan T105 is spec'd for 500 charge discharge cycles down to 25% SOC, and they define end of life at something near 75% of spec'd new capacity.

I have two trailers, one a 2004 the other a 2010, both have had GC2's in them they both get 25+ cycles/year down to near 25% SOC and the 2004 I replaced the batteries and passed them to a friend at 10 years, he got a few more year out of them. the 2010 trailer still has the original batteries. So far I have run 3 sets of GC2's each with 250+ charge discharge cycles to 25%SOC plus many to around 50% and still were meeting my needs. The important thing is do NOT leave them discharged for more than a few days, get them FULLY charged (and that means do NOT rely on the common WFCO charger in trailers it will NEVER get them fully charged)

Not to the OP, get a good battery monitor that will measure actual discharge/charge amp hours, don't rely on battery voltage to determine an accurate state of charge.

[jdc1]

Uh....yep. Fully charged should read 12.6-.7....Just like a 12V battery. That's measured at the battery.....

[Boon_Docker]

Yes, you are killing your batteries.
11.8 is 30% SOC
Should never let the batteries get below 12.1 (50% SOC)