6 volt vs 12 volt batteries for boondocking

First off you are wrong...fact...battery is made by East Penn, not interstate.

interesting.. my contact at interstate said they supplied duracell brand.. hmmm.. i need to make another call..

Second, how do you know how much solar is enough? Are you ASSuming I am going down to 50% SOC EVERY DAY? I am not.

only you know that as you didn't post your daily w/hr.

if you would care to post your daily w/hr then I would gladly discuss and assist you with panel/battery best practices.

i made a rough back calc based on battery capacity, no need to get belligerent about it..

I have been an ASE master tech since 91 and a field service engineer in the semiconductor industry for the last 22 years.
I didn't just guess when I added these components.

I'm sure you did, however paralleling always raises a red flag in the professional world, unless there is no better solution, paralleling is the last choice. I have 40 yrs as MSEE with 20 of those yrs as PE.. as you will appreciate, our design criteria will be quite different.

for this example your batteries numbered 1,2 and 3 are connected in parallel string with the take off on battery 1 to your equipment.

If you think that's how it's done, you're doing it wrong


I KNOW that's the incorrect way, I was highlighting that method for the OP's education.

you now discharge at 90 Amps. you would think that each battery will supply 30 amps right ?.. well your wrong,

Wrong only if the wiring is wrong.

you will be surprised to learn that even if they are connected as you post, the batteries will still be imbalanced ( to a lesser degree ) due to the internal resistance and capacity.

OldSmokey wrote:

marcsbigfoot20b27 wrote:

OldSmokey wrote:

All 3 of my batteries were bought in the same month....just adding them to the trailer permanently with some 1/0 cable.

not going to make much difference, 2-3 years max and you will be replacing them anyway..

Oldsmokey, still waiting to hear your reason why my brand new AGM batteries will only last 2-3 years?????

sorry for the delayed reply, I have been overseas finishing up a contract.

now back to your issue, i'll try to keep it in laymans terms.


your Duracell agm is a budget agm made by interstate, it's a 'b' grade and not
made to the best standard. battery to battery variance in internal resistance and
capacity is the issue here, when you connect them in parallel the set will behave
( performance wise ) as the worst battery. so in effect you had 2 good batteries
and one not so good and made them into three not so good batteries.

now the situation becomes worse when you actually use them and start to charge and discharge

over time.

for this example your batteries numbered 1,2 and 3 are connected in parallel string
with the take off on battery 1 to your equipment.

you now discharge at 90 Amps. you would think that each battery will supply
30 amps right ?.. well your wrong,

in practise, more current will be drawn from batt 1 than batt2 and batt 3
this is due to cable and internal resistance.
i won't bore you with complex network analysys, but the current distribution
from a 3p string is approx like:

batt 1, 41 A
batt 2, 28 A
batt 3, 21 A

so you have batt 1 doing much more work than batt 2 and batt 3
this also happens when charging, batt 1 will charge first with the others lagging
behind. now, after many cycles of this abuse, batt 1 will age much more rapidly than
batt 3. as batt 1 ages, it has the effect of dragging the others with it as they
attempt to equalize each others voltages. batt 1 drags batt 2 and 3 and batt 2 drags 3


now for fun, just imagine what happens if one battery cell develops a short ??

you guessed it.. the others dump their charge into it at a very high rate
and you get your very own firework show..

now there is a 'trick' that will mitgate some of this and it's simple..
you connect all 3 in parallel and draw positive from one end of the string
and neg from the other.. now you only have one batt underworked..
it's still not good but will give the string a better chance..


you stated you have 360 W of panels..
I can tell you right now that's not enough.. 300Ah of agm will need
at least c/10 to charge. a good mppt cc will be 90% so 360 * 0.9 = 324 W
and 324 W at 12V = 27 Amps.. so you are short even at max insolation.
you need a minimum of c/10 or better still, for agm c/6 = 50 Amps
so you need more like 720 W or so.. and that's probably wrong because we don't know
your actual usage.

and fwiw, that WFCO convertor is not woth the space it occupies and will not
charge your agm's correctly either.

if anyone needs more info on solar/RE i would be more than willing to assist.

First off you are wrong...fact...battery is made by East Penn, not interstate.
Second, how do you know how much solar is enough? Are you ASSuming I am going down to 50% SOC EVERY DAY? I am not.
I have been an ASE master tech since 91 and a field service engineer in the semiconductor industry for the last 22 years. I didn't just guess when I added these components.
You can see it here. https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29379975.cfm

OldSmokey wrote:
for this example your batteries numbered 1,2 and 3 are connected in parallel string with the take off on battery 1 to your equipment.

If you think that's how it's done, you're doing it wrong.

Wrong (both external connections to the same battery. Consider the pairs to be single batteries, this is just the clearest drawing easily found):


Right (external connections at opposite ends, so there's an identical voltage drop to each battery):

you now discharge at 90 Amps. you would think that each battery will supply 30 amps right ?.. well your wrong,

Wrong only if the wiring is wrong.

marcsbigfoot20b27 wrote:

OldSmokey wrote:

All 3 of my batteries were bought in the same month....just adding them to the trailer permanently with some 1/0 cable.

not going to make much difference, 2-3 years max and you will be replacing them anyway..

Oldsmokey, still waiting to hear your reason why my brand new AGM batteries will only last 2-3 years?????

sorry for the delayed reply, I have been overseas finishing up a contract.

now back to your issue, i'll try to keep it in laymans terms.


your Duracell agm is a budget agm made by interstate, it's a 'b' grade and not
made to the best standard. battery to battery variance in internal resistance and
capacity is the issue here, when you connect them in parallel the set will behave
( performance wise ) as the worst battery. so in effect you had 2 good batteries
and one not so good and made them into three not so good batteries.

now the situation becomes worse when you actually use them and start to charge and discharge

over time.

for this example your batteries numbered 1,2 and 3 are connected in parallel string
with the take off on battery 1 to your equipment.

you now discharge at 90 Amps. you would think that each battery will supply
30 amps right ?.. well your wrong,

in practise, more current will be drawn from batt 1 than batt2 and batt 3
this is due to cable and internal resistance.
i won't bore you with complex network analysys, but the current distribution
from a 3p string is approx like:

batt 1, 41 A
batt 2, 28 A
batt 3, 21 A

so you have batt 1 doing much more work than batt 2 and batt 3
this also happens when charging, batt 1 will charge first with the others lagging
behind. now, after many cycles of this abuse, batt 1 will age much more rapidly than
batt 3. as batt 1 ages, it has the effect of dragging the others with it as they
attempt to equalize each others voltages. batt 1 drags batt 2 and 3 and batt 2 drags 3


now for fun, just imagine what happens if one battery cell develops a short ??

you guessed it.. the others dump their charge into it at a very high rate
and you get your very own firework show..

now there is a 'trick' that will mitgate some of this and it's simple..
you connect all 3 in parallel and draw positive from one end of the string
and neg from the other.. now you only have one batt underworked..
it's still not good but will give the string a better chance..


you stated you have 360 W of panels..
I can tell you right now that's not enough.. 300Ah of agm will need
at least c/10 to charge. a good mppt cc will be 90% so 360 * 0.9 = 324 W
and 324 W at 12V = 27 Amps.. so you are short even at max insolation.
you need a minimum of c/10 or better still, for agm c/6 = 50 Amps
so you need more like 720 W or so.. and that's probably wrong because we don't know
your actual usage.

and fwiw, that WFCO convertor is not woth the space it occupies and will not
charge your agm's correctly either.

if anyone needs more info on solar/RE i would be more than willing to assist.

The EXACT positive plate thickness is a manufacturer specification. When I examined that battery I found clues not hard data. My 2013 finding provided compelling clues. Your bumped response above is what prompted me to pursue the data. I am loathe to present clues as being hard data.

Believe what you wish :)

You can do your own clue uncovering.

Perform a BCI recognized CCA test on the two samples. 50% of OEM rated CCA in amperes discharging for 15 seconds.

Perform an impedance test on both units.

A CCA test performed on my light 31 revealed a CCA rating of 630 amperes which was conducted at a temperature of around 65F

An inversion of an impedance test was the Lifeline battery accepts 103 amperes at 14.4 volts.

-------------------------------------------------------------------------------------------------------------------------

Is not the ultimate goal to have a product satisfy your own demands? If it works for you that's great. My great limitation is I cannot warranty a 30 day or 30 year battery. That heavily skews my product performance demands. From light bulbs to clothes to appliances that are not available down here, I have to stick with stuff that stays working. I wish it was otherwise.

MEXICOWANDERER wrote:
I wish I knew the positive plate thickness of the fullriver battery. But weight vs amp hours versus CCA should serve close enough to compare it to the Lifeline.

David .... here's comments you posted on 04/22/17 at 09:56pm.

Your comments in your 2nd sentence above are why I believe that the 72 lb. Fullriver is very close in capability to the 74 lb. Lifeline.

By the way, Fullriver's AGM batteries carry a 7 year warranty:
https://www.solacity.com/fullriver/

Lin, provided that information which I subsequently verified by telephoning an engineer friend at a battery manufacturing plant. The Fullriver, battery is made in China.

In 2013 I tore into a junk Fullriver group 24. Stripping mats from plates was a mess. With dial calipers I measured .035 or so (memory) to .039 with about 10 measurements. Sorry to be so vague but I neglected to commit data to memory.

And no, there was not an inordinate amount of material in the mats nor in the sediment chambers. That finding is what convinced me to go to Lifeline and never look back.

You do realize "proprietary information" is the sacred cow of competitive manufacturing? If you are truly interested in getting a better handle on your question, contact Concorde battery company and ask "Do you have competitors that have plates greater than .060" thickness". They may decline to answer. In that case refer to the Lifeline PDF manual.

As far as I know, Concorde and Rolls battery are the sole two manufacturers who state plate thickness for all to see. Doesn't take much imagination to see why they do it.

Summary: Even if the Fullriver was 50% of the cost of a Concorde, I would still go with the latter. It has to do with the unavailability of a warranty or getting a replacement down here. I do not wish to save money and lose in the end.

MEXICOWANDERER wrote:
The Lifeline has .090" positive plates, the Fullriver you use has .040" plates. Apply 14.4 volts unlimited capacity to your Fullriver. Now do the same to a 31 Lifeline. Seeing is believing. The Lifeline will accept close to 100 amperes. Essentially a C1 rate. The Fullriver? Hmmm.

David,

Where can I go to see that Fullriver plate thickness value of 0.40" that you mention? I'd like to confirm which of their models uses that thickness. About a year ago when we last discussed Fullriver battery plate thicknesses, you (and I) couldn't find that piece of information.

I've never pushed my Fullriver AGMs with the recharging equipment necessary to see how close they could come to a C1 recharge rate. The best I've seen to date is during our last drycamping trip this past June. I had discharged the RV's two of them in parallel down to around 12.1 volts. I started up the Ford V10 and let it idle. The ammeter monitoring the Fullrivers went to slightly over 70 amps (very little was turned on in the engine compartment or RV). Not bad for an idling 130 amp alternator system. Perhaps rev'ing up the engine would have shown on the ammeter more current going into the hungry batteries.

I'm not sure I see how plate thickness is related to recharge rate? I would think that is more related to internal battery resistance combined with the capability of a charger to maintain 14.XX volts on the battery terminals while simultaneously supplying whatever current that dynamic internal battery resistance dictated in real time.

As you know, I chose Fullriver over Lifeline because of the Fullriver float voltage being the proper match to my 7345's nominal output voltage - the slight price difference between the two was not an issue.

Here's the exact Fullriver and Lifeline 12V deep cycle AGM battery models I had in mind for comparison purposes when I posted earlier. (Note the error in my earlier post - the Lifeline weighs 74 lbs., not 75 lbs.):

http://www.fullriver.com/products/admin/upfile/DC120-12B.pdf

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

pnichols wrote:

MEXICOWANDERER wrote:

Oooooo and dat's the rub.

There are no group 24 and group 27 batteries that have the .070" plate thickness of the most puny GC220.

Or any of the AGM batteries having anywhere near the plate thickness of the Lifeline.

Or larger batteries having .330" plate thickness of my Rolls cells.

David ... be careful about the Lifeline plate thickness as being the head-and-shoulders champion. Note that we do not know the thickness of the plates in my Fullriver AGM Group 31 115 AH batteries, which weigh a little over 72 lbs. each ... while the 130 AH AGM Group 31 Lifeline batteries weigh arouund 75 lbs. each. Which means that the amp-hours per unit of lead volume of the two brand names is VERY CLOSE. Dividing 115 by 72 equals about 1.60 amp-hours per lb. for the Fullrivers, while dividing 130 by 75 equals 1.73 amp-hours per lb. for the Lifelines.

The Lifeline does indeed win (very) slightly in energy storage per volume unit of lead ... but certain potential buyers of the two brands would have to be able to tolerate the two down-sides of the Lifelines over the particular Fullrivers I'm comparing them to before going with the Lifelines. All this means that plate thickness of the two brand names is very close to the same - since both battery brands are of about the same Group 31 dimensions.

I will try to be quite objective and reserved. The Lifeline has .090" positive plates, the Fullriver you use has .040" plates. Apply 14.4 volts unlimited capacity to your Fullriver. Now do the same to a 31 Lifeline. Seeing is believing. The Lifeline will accept close to 100 amperes. Essentially a C1 rate. The Fullriver? Hmmm. How an it be possible for a battery with a significantly higher CCA rating have a significantly inferior charging (ampacity) acceptance?

Measure 10 square inches of glass mat from each battery. Immerse in 1.300 SG electrolyte. weigh both. Then measure mat thickness. The Lifeline has a significantly inferior CCA rating as compared to the Fullriver. Keep in mind that hugely superior charge acceptance.

Plate alignment in the Lifeline is >.001< due to laser robotics. Misalign plates just .005" and see what happens.

There is a lot more involved in producing a good battery than weight, plate count, and ampere hours. Meticulous attention to construction design specifications is one key difference between an excellent battery, Trojan and a superb battery, Rolls.

The Chinese are loathe to commit AG, silver as a grain structure modifier for grids. yet it is to be honest, quite a plus.

The Mil-Spec qualification process in the USA military would not approve of many absorbed glass mat batteries outside of the Lifeline. Same thing for many commercial passenger aircraft.

My Lifelines are to be handed down to the kids. Call them heirlooms. I do indeed take good care of them.