Replacing my Interstate 12V Coach Batteries - considering 6V golf cart batteries

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
667
Location
San Jose, CA
I thought I would start a new thread on this even though I have posted on my battery issues in the past. Last Fall I replaced my coach batteries with deep cycle Interstates batteries from Costco.  Since I rarely boondock I thought that these would be good enough, but I think I wasted my money as these are not holding a charge for even a few days with everything I can turn off, turned off.  I measured the current out of the batteries by disconnecting the terminal and putting my ammeter in series with the batteries and the coach and find it only has milliamps. And yet, these batteries, in this state, discharge in just a few days with all things off.  It seems that the only way that this is possible is if there is an internal load and the batteries are discharging on their own.  Even thought the electrolyte has 3 balls out 4 on my hydrometer in all cells, I can only conclude that these batteries are cooked. I need to at least be able to run my refrigerator on gas for a full evening.  Now it is only good for a few hours without starting my generator.

In my situation I cannot leave it plugged in continuously so I either have to go plug it in every few days or start my generator every few days.  That isn't going to reliably happen so I need batteries that can tolerate being in a state of discharge. Isn't that possible with wet cells?

My golf cart has Trojan 6V wet cell batteries that are fully discharged or nearly so every time I use it and 2 years after buying these batteries they work like they are new.

Today I went out, originally shopping for Trojan AGM 12V batteries, despite their cost.  At my local RV shop they highly recommended that, for my situation, I should consider buying two 6V golf cart batteries and hook them in series.  He specifically recommended the Deka Promaster that we was selling for $139 each. He claims that fully discharging these will not harm them and they will have more amp-hours that the 12V AGMs wired in parallel.  The only downside that he mentioned is that the wet cell battery needs to be maintained with water to keep the electrodes covered.

What is the opinion on this amongst those of you who are more experienced at this than me?
 

Optimistic Paranoid

Well-known member
Joined
Jan 19, 2013
Posts
355
There are people here who know far more about this subject than I do, so I will let them respond to your question about 6 volt golf cart batteries vs AGM batteries.  I will only say that either of these would be a FAR better choice than so-called 12 volt "deep cycle" RV batteries, which are not TRUE deep cycle batteries.

I will  add that a battery hydrometer that relies on 4 floating balls is a joke.  Throw it away and get a REAL battery hydrometer, like this one:

https://www.amazon.com/gp/product/B0050SFVHO/ref=ox_sc_saved_title_2?smid=ATVPDKIKX0DER&psc=1

As you can see, they're not expensive.
 

Koodog

Well-known member
Joined
Dec 14, 2009
Posts
465
Location
Boncarbo, CO
Yep, 6 volt definitely will give more amp hours.
Not sure about the comment about discharge. Far as I know anything below 50% on wet cell batts means disaster. Lithium can be almost totally discharged without harm.
 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
417
Location
Texas
JoelP said:
I thought I would start a new tread on this even though I have posted on my battery issues in the past. Last Fall I replaced my coach batteries with deep cycle Interstates batteries from Costco.  Since I rarely boondock I thought that these would be good enough, but I think I wasted my money as these are not holding a charge for even a few days with everything I can turn off, turned off.


These batteries should hold a good charge for months without any draw.  typical self discharge for FLA and AGM is 1 to 2% per month

you either have a bad battery or your converter/charger is not charging.

how long do you leave the rig without shore power ?
if this greater than a few weeks then invest in a battery disconnect.


a quick test for the charger:  measure the battery voltage with the rig unplugged from shore power
then connect shore power and measure again, you should see a significant increase at the terminals


Batteries:

if you favor an AGM replacement then any of these will suffice..

AGM: for 6 Volts :-

http://usbattery.com/products/us-agm-batteries/us-agm-2000/
https://www.trojanbattery.com/product/t105-agm/
http://lifelinebatteries.com/products/marine-batteries/gpl-4ct/

12 Volts :-

http://lifelinebatteries.com/products/marine-batteries/gpl-31xt/
http://usbattery.com/products/us-agm-batteries/us-agm-31/


if you go wet ( FLA ) then any of the golf cart batteries will suffice.




 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
667
Location
San Jose, CA
Koodog said:
Yep, 6 volt definitely will give more amp hours.
Not sure about the comment about discharge. Far as I know anything below 50% on wet cell batts means disaster. Lithium can be almost totally discharged without harm.

I am sure that I discharge the wet cell Trojans in my golf cart well below 50% every time I use it and that is 1X -2X weekly for 2 years. Perhaps the issue is how long you leave it at less than 50%.  I recharge these after use.  If someone knows please comment.

 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
667
Location
San Jose, CA
solarman said:
These batteries should hold a good charge for months without any draw.  typical self discharge for FLA and AGM is 1 to 2% per month

you either have a bad battery or your converter/charger is not charging.

how long do you leave the rig without shore power ?
if this greater than a few weeks then invest in a battery disconnect.


a quick test for the charger:  measure the battery voltage with the rig unplugged from shore power
then connect shore power and measure again, you should see a significant increase at the terminals


Batteries:

if you favor an AGM replacement then any of these will suffice..

AGM: for 6 Volts :-

http://usbattery.com/products/us-agm-batteries/us-agm-2000/
https://www.trojanbattery.com/product/t105-agm/
http://lifelinebatteries.com/products/marine-batteries/gpl-4ct/

12 Volts :-

http://lifelinebatteries.com/products/marine-batteries/gpl-31xt/
http://usbattery.com/products/us-agm-batteries/us-agm-31/


if you go wet ( FLA ) then any of the golf cart batteries will suffice.

Thanks, Solarman, for this reply.  I tried to respond to this, but it didn't post so let me try again.

1.  Is discharge to less than 50% or long times between recharge more favorable to AGM or FLA?  Or, are they the same?
2.  I have more than one meter in my rig to check battery voltage/level and they all say that it is discharging 20-30% per day.
3.  If I plug in to shore power or run my generator the voltage climbs within an hour or two, so I cannot fault my charger. My conclusion is that my relatively new batteries haave gone bellyup.
4.  I read elsewhere that US Battery made both Deka and Interstate.  Is that true?  If so would I be replacing batteries that failed with others made by the same company?  Are Trojans and better than Deka?
5.  It's my habit to leave my rig unplugged and don't run the gererator for as long as one month when not in use.  Each time I turn off the swithc for coach and chassis power and also turn off the main disconnect.  That said, I know that there are some items, e.g. like the Tireminder booster that are connected directly to the battery, but draw milliamps of power.
6.  Given that 6V golf cart batteries seem to have more amp hours I am favoring them and you say that all brands are equivalent.  I didn't find that to be the case between Interstate and Trojans in my golf cart, but am wondering about Deka vs Trojan.  I don't want to make another investment I will regret.
7. I don't find that FLA is such a hassle, especially if I add one of those filling systems that doesn't allow it to be oveerfilled.

Thanks again!



 

Larry N.

Well-known member
Joined
May 26, 2010
Posts
7,735
Location
Westminster, Colorado
...about 6 volt golf cart batteries vs AGM batteries.  I will only say that either of these would be a FAR better choice than so-called 12 volt "deep cycle" RV batteries, which are not TRUE deep cycle batteries.
There are actual TRUE 12V deep cycle batteries, but they are more expensive than the typical "golf cart" battery. The ones that are not are often labeled something like "RV/Marine," and they are less expensive, but lack the capacity (for RV-style use) of a TRUE deep cycle, whether 6V or 12V.
 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
667
Location
San Jose, CA
Larry N. said:
There are actual TRUE 12V deep cycle batteries, but they are more expensive than the typical "golf cart" battery. The ones that are not are often labeled something like "RV/Marine," and they are less expensive, but lack the capacity (for RV-style use) of a TRUE deep cycle, whether 6V or 12V.

I presume that "true" deep cycle can be discharged more than 50% without long term damage.  That said, when I looked a this site from Trojan they also confirm that 50% discharge is all that you can do without shortening life to 6-9 months.

https://deepcyclebatterystore.com/how-to-maintain-batteries/

I would like to under the chemistry of what happens when one holds a battery at such a level.  I would think that at such levels there is less acidity and therefore less corrosion to the cells, but experience says otherwise.  That means that some other mechanism is coming into play.
 

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
73,533
Location
At our Silver Springs FL home
I've written a magazine article on RV house battery selection that you might find helpful. There is a copy in the Forum Library at http://www.rvforum.net/miscfiles/Choosing_right_battery.pdf


First of all, it is not true that 6v have more amp-hours than 12v's. It all depends on the physical size of each and the amount of lead inside. The lead-acid battery chemistry is identical. A pair of Group 27 size 12v deep cycle will produce the same AH as the smaller GC2 6v (about 201 AH) and a pair of Group 29/31 12v produce the same AH as the heavy duty GC2 6v's (about 230 AH).


The tradeoff is that the 12v deep cycles are specialty types produced in low volume and priced higher than the more common GC2 golf car battery. That makes a 6v flooded cell more attractive from a price perspective.  However, if you go to the pricier AGM construction, 6v and 12v are similar in price on a per-amp-hour basis, so take your pick of voltage.

It is NOT true that AGM batteries can be discharged to zero (or anywhere near that) without shortening their life.  Ditto for 6v golf car batteries.  They both hold up much better than automotive batteries and the Marine/RV hybrids type, but they are not impervious to abuse.  The way to think of it is that they will last longer, but they still prefer to be discharged no more than around 50%. 
 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
417
Location
Texas
Heli_av8tor said:
Any experience or insight on the FullRiver DC260-12 AGM battery?

Tom

we call those "hernia packs".. at 175 lbs it's a big battery which is about as big as you can go with 12 Volts
that's why 2/4/6 V lighter batteries are favored.

it's a good battery, just really heavy and big in size.. oh and at $725 ea.. a bit pricey for 260 Ah capacity




 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
667
Location
San Jose, CA
Gary RV_Wizard said:
I've written a magazine article on RV house battery selection that you might find helpful. There is a copy in the Forum Library at http://www.rvforum.net/miscfiles/Choosing_right_battery.pdf


First of all, it is not true that 6v have more amp-hours than 12v's. It all depends on the physical size of each and the amount of lead inside. The lead-acid battery chemistry is identical. A pair of Group 27 size 12v deep cycle will produce the same AH as the smaller GC2 6v (about 201 AH) and a pair of Group 29/31 12v produce the same AH as the heavy duty GC2 6v's (about 230 AH).


The tradeoff is that the 12v deep cycles are specialty types produced in low volume and priced higher than the more common GC2 golf car battery. That makes a 6v flooded cell more attractive from a price perspective.  However, if you go to the pricier AGM construction, 6v and 12v are similar in price on a per-amp-hour basis, so take your pick of voltage.

It is NOT true that AGM batteries can be discharged to zero (or anywhere near that) without shortening their life.  Ditto for 6v golf car batteries.  They both hold up much better than automotive batteries and the Marine/RV hybrids type, but they are not impervious to abuse.  The way to think of it is that they will last longer, but they still prefer to be discharged no more than around 50%.

So if I understand you correctly, the golf cart batteries are less expensive therefore it might be said that for the same price you can get more amp hours with 6V golf cart batteries with the golf cart batteries at this capacity being relatively less expensive.
 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
417
Location
Texas
1.  Is discharge to less than 50% or long times between recharge more favorable to AGM or FLA?  Or, are they the same?

A: discharge below 50% for lead acid diminishes cycle life rapidly. long times between recharge is a death sentence for both types.
    prolonged exposure to partial states of charge will accelerate sulfation.
    it is actually better to overcharge a little than let cells sit in a partial state.

2.  I have more than one meter in my rig to check battery voltage/level and they all say that it is discharging 20-30% per day.

A: your battery is toast OR you have "phantom" loads discharging. 20 to 30% per day is abnormal.

3.  If I plug in to shore power or run my generator the voltage climbs within an hour or two, so I cannot fault my charger. My conclusion is that my relatively new batteries haave gone bellyup.

A: most likely, but a 200 Ah battery at 50% SOC will take quite a few hours to charge. running the genny for an hour won't cut it..

4.  I read elsewhere that US Battery made both Deka and Interstate.  Is that true?  If so would I be replacing batteries that failed with others made by the same company?  Are Trojans and better than Deka?

A: East Penn make the Deka brand, Interstate does not make batteries they re-brand. US Battery is a good second to Trojan.
In my opinion, Trojan is the better battery by a small margin.

5.  It's my habit to leave my rig unplugged and don't run the gererator for as long as one month when not in use.  Each time I turn off the swithc for coach and chassis power and also turn off the main disconnect.  That said, I know that there are some items, e.g. like the Tireminder booster that are connected directly to the battery, but draw milliamps of power.

A: For that period of time I would suggest a battery disconnect. milliamps add up over time but if you are in the 20 or 30 mA range then
battery self discharge will be greater.

6.  Given that 6V golf cart batteries seem to have more amp hours I am favoring them and you say that all brands are equivalent.  I didn't find that to be the case between Interstate and Trojans in my golf cart, but am wondering about Deka vs Trojan.  I don't want to make another investment I will regret.

A: they don't really have more Ah, it's down to size. A 6 Volt GC2 golf cart battery is almost the same volume as a Group 31 12 Volt battery.
It is half the voltage but twice the Ah capacity and has more lead per cell.

7. I don't find that FLA is such a hassle, especially if I add one of those filling systems that doesn't allow it to be oveerfilled.

A: For the amount of use you have I would suggest a couple of Costco/Sam's Club  GC2's and be done with it..
just make sure to full charge and equalize before using them. ( a sulfate layer will form over a month, you need to force it off  ) :)
 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
417
Location
Texas
JoelP said:
I am sure that I discharge the wet cell Trojans in my golf cart well below 50% every time I use it and that is 1X -2X weekly for 2 years. Perhaps the issue is how long you leave it at less than 50%.  I recharge these after use.  If someone knows please comment.

going below 50% will accelerate aging and reduce cycle life.

two times a week for two years is 208 cycles, Trojans have a 5 year calendar life, you will not use all the cycle life before they age out.

leaving a lead acid ( Pb ) battery in a partial state for long periods of time is a death sentence.

recharging after use is the correct thing to do..

 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
417
Location
Texas
JoelP said:
I presume that "true" deep cycle can be discharged more than 50% without long term damage.  That said, when I looked a this site from Trojan they also confirm that 50% discharge is all that you can do without shortening life to 6-9 months.

https://deepcyclebatterystore.com/how-to-maintain-batteries/

I would like to under the chemistry of what happens when one holds a battery at such a level.  I would think that at such levels there is less acidity and therefore less corrosion to the cells, but experience says otherwise.  That means that some other mechanism is coming into play.

SULFATION...

Sulfation occurs when the electrolyte breaks down and stratifies, sulfur ions change into free forming crystals. These crystals then stick to the lead plates of the battery forming lead sulfate crystals. Over time these crystals grow in size and become hard, covering the lead plates completely.
This significantly reduces the efficiency and storage capability of the battery.  If left untreated, you quickly end up with a boat anchor.

So...

1. never leave a Pb battery in a partial state of charge.
2. Always recharge after use to at least 90% SOC, preferably 100%
3. periodically apply an equalizing charge to "stir up" the electrolyte, it is better to over equalize a battery than to let
it sit and sulfate. over charging causes more plate corrosion, but is the lesser of the two evils.


 

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
73,533
Location
At our Silver Springs FL home
Thanks to Solarman for excellent battery advice.

I'd like to add one thing, though maybe it is nit-picking. The 50% is discharge point for lead-acid batteries is a rule-of-thumb, not a live-or-die break point.  A lead acid battery is already suffering when discharged 30% or 40%, and it just gets worse past 50%.  No need for an OMG! if the meter shows a State-of-Charge of 49% (about 12.0v), but likewise no reason to give a sigh of relief at 51% (about 12.1V). It's a case of how far and how often.
 

JoelP

Well-known member
Joined
Nov 2, 2016
Posts
667
Location
San Jose, CA
After collecting this info I went to price a Trojan 6V, but only found the appropriate size in a 12V at one local golf cart dealer.  The price was $50 more than the Deka, so I opted for the 6V Deka.  The conclusion I have reached  is that my Interstate batteries, purchased last year from Costco, were likely not true deep cycle, but rather marine batteries.  The second conclusion is that I was not sufficiently diligent about topping up the charge on the batteries--- a challenge given the rate that they discharged. 

Since I cannot plug in when storing my rig the only solution seems to be to get solar panels bigger than the tiny 10W panel that came with my RV.  If my only objective is to counteract the natural drain of the battery in storage the question is how much additional solar would be enough?  It seems that 100W would cost me about $700, but perhaps that is overkill.  I would like to hear from those who have done this, what size would be suitable.  Also would you mount them on the roof permanently or set them up on the ground next to your RV? Another alternative would be to add autostart to the generator to turn on when batteries reach a preset level.  Is that an option? A bad idea?
 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
417
Location
Texas
Gary RV_Wizard said:
Thanks to Solarman for excellent battery advice.

I'd like to add one thing, though maybe it is nit-picking. The 50% is discharge point for lead-acid batteries is a rule-of-thumb, not a live-or-die break point.  A lead acid battery is already suffering when discharged 30% or 40%, and it just gets worse past 50%.  No need for an OMG! if the meter shows a State-of-Charge of 49% (about 12.0v), but likewise no reason to give a sigh of relief at 51% (about 12.1V). It's a case of how far and how often.

True Gary, it's more of an industry reference value that is used for comparison purposes, as you reach lower values of DOD, the electrolyte has more chance of breakdown and therefore reduced lifespan. if you discharge to 100% DOD regularly you will end up with a useless battery real quick..

 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
417
Location
Texas
JoelP said:
After collecting this info I went to price a Trojan 6V, but only found the appropriate size in a 12V at one local golf cart dealer.  The price was $50 more than the Deka, so I opted for the 6V Deka.  The conclusion I have reached  is that my Interstate batteries, purchased last year from Costco, were likely not true deep cycle, but rather marine batteries.  The second conclusion is that I was not sufficiently diligent about topping up the charge on the batteries--- a challenge given the rate that they discharged. 

Since I cannot plug in when storing my rig the only solution seems to be to get solar panels bigger than the tiny 10W panel that came with my RV.  If my only objective is to counteract the natural drain of the battery in storage the question is how much additional solar would be enough?  It seems that 100W would cost me about $700, but perhaps that is overkill.  I would like to hear from those who have done this, what size would be suitable.  Also would you mount them on the roof permanently or set them up on the ground next to your RV? Another alternative would be to add autostart to the generator to turn on when batteries reach a preset level.  Is that an option? A bad idea?


for a maintenance charge you need to size the panel for twice the typical self discharge rate. ( typically 1 to 2 % per month )
a minimal starting point is to take the battery Ah capacity and multiply by 1%, 2% is better but this example will be for 1%

so say you have a 12 Volt 100 Ah battery ( eg: Group 31 ),  1% is 1 Amp so you need ( 1 Amp * 12 Volts ) = 12 Watts of solar
however, due to location and panel efficiency we need to multiply by a correction factor of 2.

so we now have 12 * 2 = 24 Watts.  we round up to 30 W.

a 30 Watt "12 Volt" panel can be had for $45 US
and a low cost 10 Amp PWM controller for as little at $20 US

less than $100 and peace of mind..

just scale this for other capacities..


for Amazon buyers..

https://www.amazon.com/HQST-Regulator-Charge-Controller-Display/dp/B01F5WFK5C
https://www.amazon.com/HQST-12Volt-Polycrystalline-Portable-Marine/dp/B072B5J7CF/ref=sr_1_5?s=automotive&ie=UTF8&qid=1533125754&sr=1-5&keywords=30+watt+solar+panel

 

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
73,533
Location
At our Silver Springs FL home
If you could identify the model of that Interstate battery we could tell you for sure if it was a marine/RV type or something other, but if it was a 12v Interstate, I can all but guarantee it was that type.  The Interstate 6v GC2, however, is as good as any other GC2 and a true deep cycle.

Deka 6v GC2 are also solid performers.

Your engine alternator should be charging the batteries as you drive home, so that you arrive with charged batteries unless the trip is short. Maybe not 100% charged, though.

I would permanently mount the solar panel on the roof unless you have shade to contend with at home.
 
Top Bottom