Recommended AGM battery capacity for boondocking

Oyaji · January 2021

Just picked up my 2021 320S Boondock. The dealer (200 miles away) installed a mystery battery--no-name, undefined capacity, which will need to be topped off with distilled water from time to time.

I'm suspicious, and my first Boondock upgrade will be to an AGM battery. NOT lithium for all the usual reasons.

The question is--what's an appropriate capacity in amp-hours? My boondocking plans will mainly be 5-6 days in the high plains (5500--7500 ft. elevations) of New Mexico at BLM sites (toilets only, if that) doing astronomy from mid-March through mid-November. Maximum draw will include the 12V fridge, interior lights, and the Alde system on cold nights, or the overhead fan on warm nights.

I will charge my 12V astronomical AGM batteries with a separate solar charging system, BTW. And, I will take along my mystery battery as emergency backup.

Thoughts? Thanks!

Marceline · January 2021

I would budget about 40-50aH per day as your starting point. From there you need to figure out how much power your solar panels are going to generate.

Basil48192 · January 2021

I live in Michigan and have dry-camped twice since getting my 320S with the roof-top solar panel and a 100 AH flooded cell factory battery.
Both trips were three days long. On the first, in late July, I hit about 50% discharge by the middle of the third day (measured to the best of my ability without a battery monitor). We had good sun for the first two days but rainy and overcast on the third. I used the refrigerator the entire time, the water pump, fan and some lights periodically.
On the second trip in mid October, we had very little sun and I ran the heat all night. Although I still didn't have a monitor, based on the indicator lights, I'm sure I was well below 50% by the third morning. I have a 100 AH flooded cell battery.
For this coming year, I have added an additional 200W suitcase solar panel, a Victron battery monitor, and plan to upgrade to (probably) two, 6V 230 AH golf cart batteries. I'm still trying to decide whether to buy the Trojan flooded cell batteries or go for the AGM.

MuttonChops · January 2021

Oyaji said:
Maximum draw will include the 12V fridge, interior lights, and the Alde system on cold nights, or the overhead fan on warm nights.

Is '21 a two way or 3-way (propane) fridge ? Use propane if you have it.
Get a good sleeping bag and keep Alde off while sleeping.

Oyaji said:
. . . suspicious, and my first Boondock upgrade will be to an AGM battery.
. . . The question is--what's an appropriate capacity in amp-hours?

Expect your 'as delivered' battery is 70AHr flooded (really should be labelled)
Which means you have 35AHr of real power.

Suggest at least a 100AHr AGM and solar panel to recharge (some of) it during day.
If your Fridge is only 12VDC/120VAC then . . . it is sharp pencil time to find the correct battery capacity for that many days boondocking.

DougH · January 2021

Another astrophotographer!! I like the Vmax AGMs on Amazon. Every size, once you decide whether you want an 85, 100, or 125Ah capacity, and how many of those you want if you don't have a recharging mechanism for that whole 5-6 day period.

You will likely need to replace battery tray and box as you go to the larger AGMs, but the forum also has plenty of examples of people squeezing two standard size AGMs into their tub with a little surgery as another option.

Consider getting a battery monitor (Renogy or Victron) for your current mystery battery, and spend a couple days in a nearby park to see if you go through 20, 35, or 50Ah a day.

Oyaji · January 2021

Yup. An astrophotographer, but still learning every clear night--which are few and far between in Central Illinois. https://www.flickr.com/photos/john_myers/albums/72157708237944024 . New Mexico Rules!

Oyaji · January 2021

Marceline said:

I would budget about 40-50aH per day as your starting point. From there you need to figure out how much power your solar panels are going to generate.

Yes. That's precisely the question: how much power, more precisely, how much energy, does the boondocking option really generate?

Oyaji · January 2021

Query whether, in a pinch, one can plug the trailer into the tow vehicle and charge the battery that way?

Verna · January 2021

@ Oyaji, the first step is to use as little battery power as possible. Luci lights are solar powered abc they illuminate the inside I’ve your T@B quite well in the evening and early morning. Another solar source would be outside solar pathway lights used inside. Just recharge then outside every day.

Use the water pump sparingly. Leave it off when you’re not using it.

At night, use the night time Alde heating feature. Set the thermostat low (I choose 60* to 62* at night, 68* to 70* during the day) because the Alde does use some battery power, not much, but it does need a spark to start on propane at night or during the day.

Someone mentioned use a sleeping bag at night. I have my own sleeping bag and the dogs have theirs. Get up in the morning, stuff the bags back in their stuff sack, put them behind the sofa and it’s quick from sleeping to being ready for those zombies who want to look at your T@B (maybe not so much with Covid around).

Each time you flip a switch, do you really need it? While Boondocking, do you really need the outside light on all night?

I charge 12V charging blocks during the day, and I charge my phone and other electronics at night using the charging blocks, not 12V from the battery.

Oyaji · January 2021

MuttonChops said:

Oyaji said:
Maximum draw will include the 12V fridge, interior lights, and the Alde system on cold nights, or the overhead fan on warm nights.

Is '21 a two way or 3-way (propane) fridge ? Use propane if you have it.
Get a good sleeping bag and keep Alde off while sleeping.

Oyaji said:
. . . suspicious, and my first Boondock upgrade will be to an AGM battery.
. . . The question is--what's an appropriate capacity in amp-hours?

Expect your 'as delivered' battery is 70AHr flooded (really should be labelled)
Which means you have 35AHr of real power.

Suggest at least a 100AHr AGM and solar panel to recharge (some of) it during day.
If your Fridge is only 12VDC/120VAC then . . . it is sharp pencil time to find the correct battery capacity for that many days boondocking.

1. Fridge is 12V, but it's a compressor model--allegedly more efficient.

2. I'm gonna keep Alde on at night at about 65 degrees. That's one of the main reasons I bought this trailer--I'm tired of cold nights in the back of my Ford Transit van or in the alternative, running a propane heater with the attendant risks (and it only runs about 5 hours).

3. I do have a 100W portable panel (with Renology controller) which I use to recharge the astro-batteries. I'm wondering if after the astro-batteries are charged, I could connect it in parallel to the rooftop panels without causing damage either to the rooftop panels or the portable panel?

4. Saleslady told me two months ago the delivered battery would be 70aH, but nowhere does the battery itself say that. I certainly have my doubts--heck, the thing isn't even branded!

Oyaji · January 2021

Verna said:

@ Oyaji, the first step is to use as little battery power as possible. Luci lights are solar powered abc they illuminate the inside I’ve your T@B quite well in the evening and early morning. Another solar source would be outside solar pathway lights used inside. Just recharge then outside every day.

Use the water pump sparingly. Leave it off when you’re not using it.

At night, use the night time Alde heating feature. Set the thermostat low (I choose 60* to 62* at night, 68* to 70* during the day) because the Alde does use some battery power, not much, but it does need a spark to start on propane at night or during the day.

Someone mentioned use a sleeping bag at night. I have my own sleeping bag and the dogs have theirs. Get up in the morning, stuff the bags back in their stuff sack, put them behind the sofa and it’s quick from sleeping to being ready for those zombies who want to look at your T@B (maybe not so much with Covid around).

Each time you flip a switch, do you really need it? While Boondocking, do you really need the outside light on all night?

I charge 12V charging blocks during the day, and I charge my phone and other electronics at night using the charging blocks, not 12V from the battery.

Thanks. A couple of observations:

1. The first rule of astrophotography is--no outside lights!

2. Where I go, the main "zombie" risk is the occasional astro-guy or astro-gal wanting to look at my telescopes and other gear--they won't much care about the trailer. And because we all are up until the wee hours looking at the stars, everybody tends to sleep in!

3. I really like the idea of the solar powered lights. Presently, I have lantern which I can charge (along with my phone) from my separate 100W panel, but a couple additional solar-powered lights might make sense. Then again, how much power would the T@b's built-in LED lights use, I wonder?

4. I was planning to set Alde to 65-67 degrees at night, but I'll take your advice and set it lower.

5. Water pump will only be used for an occasional shower or for cooking. I like the idea of turning it off unless needed.

pthomas745 · January 2021

There isn't anything "wrong" with an "unbranded" battery. If nothing else, it will certainly work well for a good spare for all the extra things you carry. I carry a small battery in my trailer for camera batteries/laptop charging, etc. Connect the solar panel to it every day or so, and it works well. There are some mods here that show how to use your "extra" battery to simply take over for the trailer's battery while you recharge it.

Your portable panel will certainly charge whatever you carry. It can be used to charge the trailer, if shade limits your charging ability. There are many different ways to connect to the trailer. How big are the batteries you use for your astronomy setups?

The bigger issue? Water and waste management for those longer trips. I have the "stock" battery and a 100 watt panel, and the fridge with the propane option. I can go a loooong time with as little power that I use, but eventually boondocking is over when the tanks fill. (And I'm pretty careful with them, too.)

The new fridges are getting rave reviews for power use, so the 30-40 ah a day might be a bit high, but even a fridge can be turned off to save power, since it is a pretty good cooler all by itself.

Oyaji · January 2021

pthomas745 said:

There isn't anything "wrong" with an "unbranded" battery. If nothing else, it will certainly work well for a good spare for all the extra things you carry. I carry a small battery in my trailer for camera batteries/laptop charging, etc. Connect the solar panel to it every day or so, and it works well. There are some mods here that show how to use your "extra" battery to simply take over for the trailer's battery while you recharge it.
Your portable panel will certainly charge whatever you carry. It can be used to charge the trailer, if shade limits your charging ability. There are many different ways to connect to the trailer. How big are the batteries you use for your astronomy setups?
The bigger issue? Water and waste management for those longer trips. I have the "stock" battery and a 100 watt panel, and the fridge with the propane option. I can go a loooong time with as little power that I use, but eventually boondocking is over when the tanks fill. (And I'm pretty careful with them, too.)
The new fridges are getting rave reviews for power use, so the 30-40 ah a day might be a bit high, but even a fridge can be turned off to save power, since it is a pretty good cooler all by itself.

1. For astronomy, I use two 20aH AGM's and take a 20aH spare.

2. Waste management: I will use the BLM vault toilets, or failing that (they were closed last Spring for Covid), will dig cat-holes as permitted by the BLM. I really don't want to mess with black water, which is why I got the 2021, which has a cassette toity. But I don't want to mess with that, either--I only will use it if I can talk my wife into an Alaska trip. No way she would ever dig a cat-hole!

3. Re gray water: I need to figure out a solution, but while camping in my van I have never used more than 10 gallons of water on these trips--which I have carried in plastic jerry cans. I have just "donated" the water to the thirsty high plains vegetation. They haven't complained.

Bottom line, I take it, is that you get by with the stock (presumably 70aH) battery?

Verna · January 2021

@Oyaji, in order to find out what each switch operated unit uses in power will require mathematics on your part. How many aH do the Led lights use? I’ll let some of the mathematic pros here tell you the formulas.

I can keep the temp lower at night because I do use a sleeping bag on a self inflating mattress pad on top of the cushions. I’ve tried the nice sheets and quilt and blankets, and I decided to go back to simple. I stay warmer, hence not as much Alde heat needed. If you sleep in in the morning, even less heat is needed on sunny days as the sun will help heat it up inside.

pthomas745 · January 2021

The difference in my power use would be the fridge that can run on propane, not battery power. I will upgrade to a 100AH AGM.....but I can't get my original battery to die......and I haven't been camping at all for the last year. I do miss the meteor showers and trying to get better at Milky Way pictures.

The best reason to increase battery capacity is for better fridge power management. Sounds like you are pretty experienced with long term camping without "facilities" and have a decent handle on solar power use for the small AGM's. The trailer will be much more comfy, and those solar skills can be put to good use. Been a while since I went to a star party, and, since it was dark =)I didn't get a good look at the power needs of some of the equipment.

DougH · January 2021

@Oyaji Beautiful flickr collection and setup! Originally from Illinois too. Used to have a big truss scope, but cut waaay back to a triplet 90mm wide-field refractor for RV travel, and only bring a laptop so I can run Siril (simple postprocessing). There's half a dozen or more astronomy minded T@bbers on the forum, though I've yet to see a T@B at a star party.

jkjenn · January 2021

You are looking at about 3.5-4.5ah with just the fridge and phantom power draw.

I am still experimenting with my 2 6v AGM battery set up and solar, but the 105w panel on the Boondock is not enough to keep up.

I have picked up.an additional 100w panel and charger but didn't get a chance to try it before the solar max values dropped for the winter.

I tried the Smart Energy module for the fridge from Isotherm, but it doesn't work. The fridge never turns off with it and my food all froze, so I will be having it removed.

The fridge is very efficient, but you need a little more solar than what we T@b owners have got away with in the past.

Verna · January 2021

@jkjenn, I’ve always went by the rule of keeping my batteries’ aH as close to the number of watts of solar as I could. The 2014 T@B S Max had 235 aH of batteries and 200 watts of glass portable solar panels. It did well.

The 2019 T@B 400 had 235 aH of batteries and 200 watts of flexible solar panels on the roof, plus during one really low solar event, I added my 200 watts of glass portable panels. It did well.

My 2021 T@B S has 235 aH of AGM batteries and 310 watts of flexible solar panels. I can also add my 200 watts of glass portable solar panels. Obviously, I do not want to run out of power! The Smart Shunt shows the solar panels are keeping the batteries full, even though the larger panel is partly shaded. The battery switch is turned off, so no phantom battery draws are taking power from the batteries.

Marceline · January 2021

@Oyaji
Most people on this forum have 3way fridges so be sure to filter the feedback you receive. @Verna and @jkjenn are giving you good advice.

I have clamshell T@B which means that I have a 2way fridge (although not an Isotherm). The 2ways consume about 3-4aH while running. So assuming they run about 30% of the time, the fridge alone is 25-30aH per day. That's going to be the biggest number. After that comes Alde, lights, water pump. If you use the fan (unlikely in winter) that could be another big number. So that's why I suggested you budget 40-50aH consumption per day. I don't know how much power you can get out of the factory solar - especially in winter. You really need to get a handle on that number. For me, I didn't want the added tongue weight of 200aH of conventional batteries to get 100aH of usable power, so I bit the bullet and got a lithium battery. YMMV.

Solar powered lights of all sorts are great to have. I have some Luci lights and also some cheap Ikea solar powered string lights. I also use one of those lithium jump-starters as a back up power supply for recharging my cell phone.

Oyaji · January 2021

Wow. Lots to ponder here. But the bottom line is that I'm just gonna have to pick a system, try it out and see if it's sufficient. I'm thinking 100 aH AGM battery from a reputable (and hopefully not Chinese) manufacturer, with my mystery battery as a backup.

kbdigitiqe · January 2021

@Oyaji Don’t want to start a firestorm here, but I’m consistently intrigued by the intense.. ahem ... frugality of the majority of members on this forum.

I mean Tabs are not cheap campers. Y’all just paid $25k+ for a teardrop right? Likely have a $30k+ tow vehicle? $1,000 more on a good Li setup and you can literally disregard every other post in this thread and on this entire forum about how to be constantly obsessed over how much battery this and that uses.

Because like you, we only Boondock, we made the switch to Lithium and we haven’t thought about our battery since, it just works all the time and has never come close to draining on a 5-7 day trip, with a little sun it’s pretty much infinite.

Now we just camp, wherever we want... which was the point of the whole thing anyway.

johnfconway · January 2021

Oyaji said:

Yup. An astrophotographer, but still learning every clear night--which are few and far between in Central Illinois. https://www.flickr.com/photos/john_myers/albums/72157708237944024 . New Mexico Rules!

This may partly explain why we've been seeing so many T@Bs going by the back of our property on Hwy. 90 (road into Silver City, NM off of I-10 coming from west). It can't just be that our eyes are more attuned to shape and features.

If it's too cold up in the 4 corners area, we have an International Dark-Sky Sanctuary site in the Gila National Forest named "Cosmic Campground". https://www.fs.usda.gov/recarea/gila/recarea/?recid=82479

https://www.darksky.org/our-work/conservation/idsp/sanctuaries/cosmiccampground/

It's typically warmer down here in SW New Mexico. The not so mentioned quality about this site is availability of top-notch day hiking close by. Mineral Creek is a show to not miss https://www.alltrails.com/trail/us/new-mexico/mineral-creek-trail, as is "The Catwalk" https://www.newmexico.org/places-to-visit/regions/southwest/catwalk/

Sharon_is_SAM · January 2021

@kbdigitiqe - there are times when you don’t have much sun to recharge. That’s when it pays to have extra battery capacity and to know your draw down limits. Not everyone wants to spend another $1000 on lithium. Eventually lithium will be the standard, but there are still a lot of us using perfectly good lead acid batteries. Maybe for some of us it means more tongue weight and less sway😁. That’s another thing we obsess about!

DougH · January 2021

It's also early days to know the impact of "White Oil" in countries like Portugal. On my next camper (400? 540?) I'd love a few heated Battleborns, but I worry which kind of RV battery will have the best recycling with least harmful exposure to people who work in those recycling centers.

https://www.forbes.com/sites/rrapier/2020/01/19/environmental-implications-of-lead-acid-and-lithium-ion-batteries

kbdigitiqe · January 2021

Yah, my point was once we spent the $1000 on Lithium, we haven’t cared since if the sun comes out because it almost doesn’t matter anymore, battery life is virtually a non issue.

My second point was, especially if all you do is Boondock, $1000 is not even half of the sales tax alone on the brand new 2021 Tab 320 they just bought.

Verna · January 2021

kbdigitiqe said:

Yah, my point was once we spent the $1000 on Lithium, we haven’t cared since if the sun comes out because it almost doesn’t matter anymore, battery life is virtually a non issue.

My second point was, especially if all you do is Boondock, $1000 is not even half of the sales tax alone on the brand new 2021 Tab 320 they just bought.

I ordered my 2021 T@B S Boondock in June of 2020. All of the talk then was how to keep those current lithium batteries warm. Living in Indiana would have meant to move the batteries into my house frequently. Then, later this fall the talk was about heated lithium’s. Well, my T@B was already on order, the dual AGM’s were installed and just waiting on the back ordered items. I received my T@B on Nov 7th, and in 5 to 7 years, the lithium or whatever the newest and greatest batteries will have made a lot more headway. I will have gotten my investment in the AGM batteries back, and I will have done a lot of camping, mostly with just the flexible solar panels on my roof charging my current AGM batteries. I, too, don’t have much to worry about because of what I selected, as I knew the stock solar panels were not going to meet my needs.

kbdigitiqe · January 2021

Lol remember when I started my post by saying “I don’t want to start a firestorm here”

🤷‍♂️❤️

Marceline · January 2021

Oyaji said:

Wow. Lots to ponder here. But the bottom line is that I'm just gonna have to pick a system, try it out and see if it's sufficient. I'm thinking 100 aH AGM battery from a reputable (and hopefully not Chinese) manufacturer, with my mystery battery as a backup.

100aH AGM battery = about 50aH useable power. That's less than 2 days worth of power with zero recharging. This is why it's so important to guesstimate what your solar will generate. If you don't want to invest in 100aH of capacity (100aH lithium or 200aH conventional) you might want to consider getting a generator. Another alternative is to give up on using the refrigerator.

Verna · January 2021

@kbdigitiqe, no firestorm from me. Just an explanation of how 2 months of daily research gave me the answers I wanted at the time, but by the time I received my new T@B, the market had shifted to heated lithium batteries that were not mentioned as being reliable when I started my research. But that’s OK as I’m happy with my T@B, and I’m sure there will be other battery choices in 5 to 7 years when I’m ready for new batteries. Technology keeps moving on!

No one had Victron products in their T@B when I got my 2014 so we all used cigarette plug-in voltage meters. The first person to add a Progressive EMS posted how to photos that are just like how it is done today. Technology grows quickly.

Marceline · January 2021

Verna said:

I ordered my 2021 T@B S Boondock in June of 2020. All of the talk then was how to keep those current lithium batteries warm. Living in Indiana would have meant to move the batteries into my house frequently. Then, later this fall the talk was about heated lithium’s. Well, my T@B was already on order, the dual AGM’s were installed and just waiting on the back ordered items. I received my T@B on Nov 7th, and in 5 to 7 years, the lithium or whatever the newest and greatest batteries will have made a lot more headway. I will have gotten my investment in the AGM batteries back, and I will have done a lot of camping, mostly with just the flexible solar panels on my roof charging my current AGM batteries. I, too, don’t have much to worry about because of what I selected, as I knew the stock solar panels were not going to meet my needs.

@Verna makes some good points. I'm in California so charging temperature isn't a big consideration for me. I was able to get a non-heated drop-in replacement 90aH lithium (LiON Energy) for about $700. The math worked out for me at that level. But the heated lithium batteries cost a fair bit more.

jkjenn · January 2021

Agree with a number of the comments, here. Lithium is not always the best solution and isn't always about money.

I would add, that a 100ah battery and the stock solar won't be enough to keep up with the phantom and fridge usage, let alone give you usable battery capacity with T@bs running the Isotherm fridge if you want to dry camp for more than a day or two.

Verna's suggestion about sizing solar to battery capacity is spot on. I got away with the 133w solar panel on my 2015 T@b and using the fridge on LP. On my 2021 320, the solar panel is 105w. I need that second panel.

Sharon is also right about possibly not getting enough sun to recharge and needing a little extra capacity for those days.

Don't forget time of year and latitude, too. Where and the time of year that you camp has an impact on your solar yield.

It really does take some trial and error to work things out to meet your own needs.

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Recommended AGM battery capacity for boondocking

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