dual batteries - R-pod Owners Forum

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bodie55

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Joined: 25 Mar 2013
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Topic: dual batteries
Posted: 21 Apr 2013 at 1:47pm

In prepping for the big event, we've been researching dry camping. We won't have the opportunity to dry camp at home before we begin the trek back, but we can test it out at the campground we're staying at for a few days after the pick-up, close to the dealer in case there are any bugs to work out.

That being said, we've been searching the forums and have a good idea of holding tanks and propane capacity. I've read found what I can about the battery capacity and it seems like adding a second battery from the beginning might be wise. So my specific question is if we are only using the battery for the water pump, fantastic fan for ventillation, and fridge brains, is it reasonable to expect that a single battery would last for a 3-night dry campout? Is there any synergistic effect by having two batteries, or would we expect to just double the time available? We've comtemplated buying a generator (too expensive for the moment) or getting a small solar charger (I know full sun exposure would be important), but are thinking the second battery (same model, same age) from the start might be a wise investment. Any thoughts?

There are five of us, but the navy showers will work for the adults. The Giant Teen and two little kids can jump in a lake, river or pool. (GT didn't go with us on our shopping adventure for the pod and I'm not even sure if he will fit in the marine bath, but we didn't buy it for him! At 6ft and growing, this should be interesting.) The main reason I wanted my 'fancy tent' is so I can bathe. Flashlights and camp stoves are the norm for us, so using the lights and stove will be minimal no matter where we camp. We are planning to switch out the lights for LEDs.

Everyone has been so helpful so far, and we appreciate all the advice and support for the newbies. Can't wait to get the pod back home and spent the fall weekends on the coast at some random state beach and chill! Waves and tide pools await us:)

Kristy

Bay Area Crew
2013 178 Beach Pod
F-150 SuperCrew
...sempre in viaggio sul mare...

bhamster

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Posted: 21 Apr 2013 at 4:03pm

We've dry-camped on a single battery for 4 days before (no heater use) and it worked fine. So your 3 day trip should be fine... just be careful not to leave anything on. We even turn off the propane detector during the day to save power.

When you're considering your options also consider that a solar charger or generator has the ability to extend your trip almost indefinitely, but additional batteries only lengthen it a finite amount. Also remember that batteries only last a few years, but generators and solar panels will last for the foreseeable future. Personally, we only have one battery and use a solar panel and we've never gone below 2/3 on the rpod's battery meter even on a 5 day trip.

furpod

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Posted: 21 Apr 2013 at 4:11pm

We have done a full week on our dual battery setup. We were still at 12.25v or so. We have full LED lighting, and are careful about our battery use... If.. in an emergency.. you need to top up the battery.. use jumper cables from your tow vehicle battery and run the engine for an hour.. No extra effect with dual batteries, you just get double the useable amp hours.

If you expect that a dual battery setup is in your future.. when picking up your new rig, buy your second battery right then and there, so they are matched as well as possible. Ours were next to each other on the pallet..

CharlieM

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Posted: 21 Apr 2013 at 9:34pm

Bodie55,

All the above comments are good and relevant. There are many arguments for the dual battery setup. I opted for the second battery and a second 20 pound propane tank in anticipation of camping in National Forest campgrounds. I ordered the second 12 volt group 24 battery from the dealer when I picked up the pod.

However, knowing what I know now, I would do things differently. Each group 24 battery is good for about 80 ampere-hours (AH). Two batteries will provide 160 AH. But, two GC2 6 volt golf cart batteries wired in series will provide 12 volts at 230 AH, about 40 percent more. The two GC2s will fit in the same space as the group 24s and work the same electrically. The cost is a bit more, but the extra capacity is worth it, particularly when using the propane heater, the water pump, and before you convert to LED lighting. You should be able to dicker with your dealer for an exchange.

Welcome to Poddng,

Charlie
Northern Colorado
OLD: 2013 RP-172, 2010 Honda Pilot 3.5L 4WD
PRESENT: 2014 Camplite 21RBS, 2013 Supercharged Tacoma 4L V6 4WD

bodie55

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Location: San Francisco
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Posts: 100

Posted: 23 Apr 2013 at 10:23pm

Thank you for all the good feedback. We spent some time doing more research on the solar panels this past weekend. On the Zamp website, they have a picture of an r-pod with panels mounted on the roof. We'll probably opt for a portable unit, but need to decide on 40 or 80 watts.

Anyone have a advice on how long it takes to recharge the battery with solar, assuming one has direct sunlight? I'm guessing the 80 watt would be faster, as it's twice as big...

Thanks,

Kristy

Bay Area Crew
2013 178 Beach Pod
F-150 SuperCrew
...sempre in viaggio sul mare...

Keith-N-Dar View Drop Down

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Posted: 24 Apr 2013 at 5:35am

About six months if you are lucky. Unfortunately for the cost solar is not a good option if you really want to recharge a battery like on a Pod. You would need a much larger array than one of the portables. You can recharge a cell phone or computer, but the smaller arrays may not even overcome the internal resistance in a car type battery.

Keith-N-Dar
Boris & Betty (Boston Terriers)
2011 R-Pod 177
2010 Ford F-150

furpod

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Posted: 24 Apr 2013 at 8:31am

Well.. other people are way smarter than me on this but.. IF (and I say IF because it ain't going to happen), but if, you really could get "80 watts" out of your panel, that's a little over 6ah. Real battery talk revolves around amp hours. Real solar talk revolves around actual production, not rated capacity..

With a solid mount panel, no tracking mount, you will probably see an average of 1/4 or the panels rated capacity over the course of a clear day.

so 12 hours times 6.5 or so amp hours at 12v+/- is 78ah a day. HEY IT WOULD WORK!! except.. you will never see any where near that number. Maybe 20ah in real use.. and then there are resitance and conversion losses.. I would bet 15ah available to the battery over the course of the day. Couple cloudy days and you are sunk.

So, if you can keep your 12v use low, LED's for lights, no inverter action to run the TV/DVD etc, that 80 watt panel can extend your off grid time, but it's not going to stay ahead if you need to say, run the heater. The heater blower can pull near 30ah a night from your battery(s) all by itself..

I have not been to the website you mention, but there isn't very much real estate on a pod roof..

Now.. again, there is no doubt that they can, and will extend your off grid time. But for the $$ a small, good genny is the answer. The Honda inverters are the gold standard.

bhamster

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Posted: 24 Apr 2013 at 10:14am

Let me defend solar a bit...

Originally posted by Keith-N-Dar

About six months if you are lucky. Unfortunately for the cost solar is not a good option if you really want to recharge a battery like on a Pod. You would need a much larger array than one of the portables. You can recharge a cell phone or computer, but the smaller arrays may not even overcome the internal resistance in a car type battery.

No facts or figures here at all... so lets add some: I'm assuming you're talking about the self-discharge of a lead acid battery since the internal resistance is not difficult at all for any charger (20 milliohms)... lead acid batteries self-discharge at a rate of about 4% per week. For a 80AH battery, that's just 3.2AH/week. Even if your 80 watt panel only charged half of it's rated output (40 watts) that would only take an hour of sunlight to overcome (PER WEEK). If you're really concerned about that, get an AGM battery and it's almost a non-issue. As to the cost/watt of course it's going to be more than a generator, but that's not the only factor. Solar panels are silent, maintenance free, can be "running" while you're away, don't cost anything to run, and are extremely light and portable. All of those factors are worth different amounts to different people.

Originally posted by furpod

With a solid mount panel, no tracking mount, you will probably see an average of 1/4 or the panels rated capacity over the course of a clear day.

Not sure where you're getting this figure from, but solar production is usually calculated using solar insolation hours, which depend on the season. For a fixed installation it's around 4-5 solar insolation hours per day. That means with an 80 watt panel you're getting up to 33ah out of the panel. You'll lose about 25% due to efficiency losses, which gives you about 25ah to the battery. That's almost 1/3 the capacity of a group 24 battery.

Originally posted by furpod

So, if you can keep your 12v use low, LED's for lights, no inverter action to run the TV/DVD etc, that 80 watt panel can extend your off grid time, but it's not going to stay ahead if you need to say, run the heater. The heater blower can pull near 30ah a night from your battery(s) all by itself..

The furnace uses about 3 amps when it's running. You would have to run it continuously for 10 hours to get that 30ah figure. Even on a really cold night I'd say my heater is only running an hour or two total. That's only 6ah at most.

Originally posted by furpod

I have not been to the website you mention, but there isn't very much real estate on a pod roof..

They fit a 200 watt system on it...

Originally posted by furpod

Now.. again, there is no doubt that they can, and will extend your off grid time. But for the $$ a small, good genny is the answer. The Honda inverters are the gold standard.

You're right, even a nice honda is only $0.50/watt, which is 1/4 or less the cost/watt of a solar installation... but that's not the only factor. As I mentioned above, there are many advantages of a solar setup that aren't captured in a purely financial comparison.

techntrek

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Posted: 24 Apr 2013 at 2:58pm

Actually most lead-acid designs self-discharge at 2% per day in warm weather, which is why you must top them off at least once a month during the summer. AGMs have a lower discharge rate but they are rare compared to the usual flooded lead-acid used on most campers.

Off-grid solar systems come out to about a 52% efficiency of the solar panel's rating after you take into account the things that furpod mentioned plus the PV derating due to heat, battery losses during charging, etc. However, that just gives you a rough hourly figure. Then you need to take into account the "solar insolence" factor, which is roughly 4.5 to 5.5 hours of equivalent sun in most of the US. So an 80 watt panel * .52 * 4.5 = 187 watts available per day. That comes out to about 15 amps per day.

If you start off with a charged battery and use 15 amps each day AND get full sun each day, you'll have a charged battery by the late afternoon. Since you can go down to 50% state-of-charge (and 30% SOC on rare occasions), the typical 100 amp deep cycle battery would allow you to draw out 15 amps for over 3 days if you got no sun at all.

Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ Pod instruction manual

bhamster

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Posted: 24 Apr 2013 at 3:38pm

Originally posted by techntrek

Actually most lead-acid designs self-discharge at 2% per day in warm weather

How warm are we talking here? The 4%/week that I mentioned is at 80F...

We could argue about the exact figures all day, but the bigger point is that many people successfully charge their trailers with solar panels and it could work for bodie55 also.