New RV Owner - Dual 6 Volt Questions

[Trobec]

Originally Posted by TravisITGuy

this is a great discussion, i just returned from a 2 day dry camping trip and find my current 2yr old dual 12v batteries wont keep a charge thru the night. this is with nothing on in the trailer except a cell phone being charged and the co2 detector running. . I am assuming that when the fridge/freezer is on propane it requires little battery if any. I am in the market for replacement batteries and really want to go dual 6v.

Ive read on another site that Costco has a good price on a battery close in spec to the GC-2 Interstate.

Personally I would go with 2 trojan t105 6 volt battries. They do cost more but they are also a true deep cycle battery and give you around 230 amp hours. They will also last 10 years when properly maintained.

[camaraderie]

x2 on the Trojans IF you plan to dry camp and cycle your batts a lot. If you stay plugged in most of the time, the Costcos are probably the best value for the $$.
Don't forget to add in a real battery monitor to your upgrade. It will pay for itself in battery life.

[Skyliner]

Costco's and GC2 from Sam's Club are not that good. I've been running EGC2 from Sam's and they weight several pounds more than the Costcos and cheaper Sam's so far at 2 years are doing great!

[pgandw]

I use the dual Costco Interstate GC-2s. Mine were rated at 232AH each. Cost in 2015 was $75 each, sales tax included, but I got credit for the cores on my 12V batteries I turned in.

I use an installed voltmeter to monitor state of charge when dry camping, and monitor the Progressive Dynamics converter when plugged in.

All together, a low maintenance, low cost, "it just works" setup. Good for powering the A-frame for 4 nights dry camping, with up to 50% heater usage at night. No need to lug a generator or having to secure solar panels in the Colorado winds.

The only issue I have is that the A-frame fridge will blow out - no auto start - when being towed and on propane. So I have to use DC to keep fridge cool while towing - draws 10 amps. The TV charge line will supply the 10A, but very little more. Which means when we stop for lunch, gas, check-in, etc, the fridge is depleting the batteries. And the depletion will not be made up on the way to the campground.

My way around this is to let the fridge pull down to about 27-29 degrees while towing, which it will readily do in a few hours unless temps are in the 90s. Then shut off the fridge for the last couple of hours before arrival. This lets the TV top off the batteries for a couple of hours, and the fridge will stay below 40. I do monitor fridge temps with a $10 Walmart wireless thermometer.

just our experiences
Fred W
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[wannabeowner]

"1) what is the most simple way to monitor the battery so that i dont drain them down past 50%? "

I'd also like to know if there's a simple, relatively accurate way to do this. We intend to get a Trimetic or Victron monitor in the future, but it won't happen this summer. Is there another, reliable way to monitor battery usage while dry camping?

[TravisITGuy]

so i typically plug my trailer in at home after returning from a camping trip so the fridge/freezer stay cold. I also keep it plugged in thru the winter months. is this not good for the batteries?

If someone could share a link to a quality battery monitor. I appreciate the feed back everyone.

[camaraderie]

It's not a great idea in storage to leave it charging...but it's better than not topping up and storing! Suggest (when you don't plan to use the fridge... ) that you FULLY 100% charge the batteries then REMOVE the negarive battery wire. Your batts should be just fine for 3 months at least. Check voltage and recharge when you've hit 12.2V in summer and 12.4 V in winter if you are in a freeze area.
As to a monitor...try the Victron BMV700 series. The basic one is all you need to take care of the batts...but you may wish to have some of the features on the others.
https://www.victronenergy.com/battery-monitors/bmv-700
Widely available.

[Mountndream]

If the OP wants a simple solution for his batteries not dying while in storage and not having to remove them either. A simple battery disconnect is the cheapest and easiest solution (under $20)

Also, i find that a battery disconnect is the simplest and easiest thing you can do to ensure that you don't discharge your batteries to below 50% when the unit isn't in use.

[pgandw]

Originally Posted by wannabeowner

"1) what is the most simple way to monitor the battery so that i dont drain them down past 50%? "

I'd also like to know if there's a simple, relatively accurate way to do this. We intend to get a Trimetic or Victron monitor in the future, but it won't happen this summer. Is there another, reliable way to monitor battery usage while dry camping?

As I posted, I installed a voltmeter just inside the A-frame entrance door. When dry camping, the voltmeter provides an estimate of SOC. When battery voltage drops to 12.1, the battery is at approximately 50%.

Contrary to what some have posted, modest loads on a battery in decent condition do NOT impact the voltage reading significantly. In my experiment with the propane/CO detector on, the Fantastic Fan on, and any other parasitic loads on, the battery voltage dropped 0.02 volts (repeated) compared to the no-load condition. And because the load lowers the voltage, I would reach 12.1V when the battery was actually slightly better than 50%.

The 50% is not hard and fast, either. As the SOC goes lower, the number of discharge/recharge cycles the battery will tolerate before it is toast gets smaller. If you drop to 40% SOC, you get fewer discharge/recharge cycles. If you always stay above 70% SOC, you get a longer battery life - at the cost of less usable capacity. 50% SOC is simply a commonly used trade-off point between usable capacity and battery life.

These SOC vs battery cycle curves vary by the type of battery. The typical "marine deep-cycle" is actually a combination starting and deep-cycle battery. It will maybe do 100 cycles at 50%, and drops off rapidly below 50%. You car's starting battery only needs 2-3 cycles below 50% SOC, and it is toast. A Surette deep cycle can do at least 500 cycles at 50%. Gel and lithium batteries have completely different curves.

hope this helps
Fred W
2014 Rockwood A122 A-frame with 2 6V GC-2 batteries (Interstate/Costco)
2008 Hyundai Entourage minivan
camping Colorado and adjacent states one weekend at a time

[TravisITGuy]

My Evo has a battery cut off switch. I will work on using that more often.

[Mountndream]

Originally Posted by TravisITGuy

My Evo has a battery cut off switch. I will work on using that more often.

that still lets parasitic draw. ie, Carbon monoxide detector still has power. Install one on the battery cable. its super easy and cheap

[TravisITGuy]

when i turn that cutoff switch nothing in my trailer has power including the co2 detector. its a master cutoff switch.

[camaraderie]

Originally Posted by wannabeowner

"1) what is the most simple way to monitor the battery so that i dont drain them down past 50%? "

Simple no...relatively accurate yes.
Get a hyrometer that has measurements for specific gravity on it. About 10 bucks on Amazon.

So first you charge your batts overnight and then in the AM disconnect the negative wire and wait a few hours if possible. Then suck up the battery water into the hydrometer from EACH cell. They should all read around 1270 if the batt is new if ANY cells are out of whack with the readings from the other cells (lower) then there has been sulfation and lost capacity in that cell. You need to have a shop put an equalizing charge (caps off...15V+) to see if they can be brought up to capacity.
Now...write down the readings you got from each cell...those are your baseline measurements AT the current temperature.
Now when you're out camping, you don't want to let the specific gravity fall below the 50% level which is 1170 at 80 degrees. So you take measurements again to get new cell readings to get a good idea of your state of charge. In practice I'd just check one cell...and if it is well higher than 1170...forget the rest for now.
Once it gets to 1170...check a couple of other cells to make sure everything is around 50% and recharge TO 100%. This will take at least 6 hours with a good modern charger of sufficient size.

On short camping trips, many will cycle between 80% full and 50% full because "recharging to 80%" only takes a couple of hours. It you do this...be sure that at LEAST once a week you recharge to 100%. And ALWAYS before you store your unit...get to 100%
Your batts will thank you.
If you do this all summer...maybe Santa will bring you a Victron for being a good boy!



BTW...heres a specific gravity chart for any hydrometer. You need to add 4 to all readings for temperatures below 80 degree...for every 10 degrees cooler. Subtract 4 for each 10 degrees warmer to get true state of charge.