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Doesn’t make sense to me because it’s an oversimplification. Early in my career there were many “rules of thumb” as they were called then that often led to bad designs because they were taken out of context.

This would be OK if all AGM and LiFe batteries were around 100 Ah, and granted most are, but all are not which opens door to mistakes. An 80 Ah AGM is far from a 255 or 330 Amp-hour AGM. I know what you mean, but the new guy may not.

For that matter, we need to get people to stop thinking of battery capacity solely in Amp-hours, but that’s a different issue; and one that may take years to change if it ever does.
You are right:

- I purposely did not want to confuse people by bringing in the need to look at battery discharge curves into the discussion. Yes, I have those plots in my computer and have played with these curves and various power implementations.

- I simplified the discussion by focusing on 12 volt, size 24 - 31 AGM and LiFe batteries in the 80 - 110 amp-hr range because that is a common size in van conversions (and what I use in projects).

- People can physically lift this size range of batteries without too much trouble. Larger sizes are challenging to handle, at least at my age. An 8D battery is amazing, but I can't lift one so it doesn't make sense for me to recommend this to anyone else.

- In size 27 you can buy both AGM and LiFe from multiple suppliers, with reasonable specs, so IMHO, that is a reasonable size to use. I fact, that is what I use and do recommend it to people.

- The only AGM battery that I use is Lifeline but there are a couple of other similar ones out there. I am not a dealer, just very familiar with their performance and fit. If someone thinks that they can buy a $50 battery and get similar performance, not much that I can do to help them. I have lowered my expectations that people will or will not accept my suggestions and don't enter these types of discussions about battery selection. Either they are willing to read a data sheet - or not.

- I am not sure if size 27 is the perfect intersection of price / performance / ease of use, but it isn't so far from it that people will say "you are an idiot - size xxx is 10 x better".

- For me personally, I much prefer to use the term "usable capacity of xx kW-hrs" instead of amp-hrs, partially because I prefer to use 48 volt and 24 volt systems, but that is a different matter.
 

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To save your battery state of charge during running the microwave you could start the van and run it for 5 minutes while the microwave is running that way your alternator powers the microwave instead of drawing down your precious battery.
This will work because of the small runtime of 5 minutes or less.
Won't work with trying to power a Air conditioner or battery charger because of the long runtimes will eat into your gasoline bill.
Unless you'd be driving anyway , example long trips.

Me personally,, my microwave run times are more around 30 seconds
Sometimes 60 seconds.
If I buy a frozen tv dinner I let it thaw over night , next day cuts the run time down.
 

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Harry, I knew exactly what you were implying, and agree with numbers. I was just concerned non-technical guys may not even think of the differences in ratings. Looking back it’s obvious that the simple 6V versus 12V Amp-hour difference has led to bad choices for some buyers.

For what it’s worth, at Tampa RV Super Show I was interested in seeing the new Coachmen Cross Trek that has no generator, but instead a 3,000-Watt Xantrex inverter powered by single 330 Ah AGM battery. Like you, I figured it would need about 600 Amp-hours, so 2 X 330 Ah batteries (or equivalent).

Turns out there was enough room underneath for a second ~180-pound battery. That’s one heck of a battery though. On the next floorplan at show, the 21XG, Coachmen went with 4 X 100 Ah, with possible room for 2 more for a total of 600 Ah.

I know one large battery may save a little cost and weight (not even sure of that), but also agree with you that a 4D or 8D lead battery isn’t easy to handle. And if it fails, you lose a lot all at once.
 

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P.S. — Another option I noticed at Tampa Super Show is use of a dual-purpose AGM. If looking to run high-power devices for a short period without running battery to low state of charge, a dual-purpose battery may work better in supplying high current for a few minutes at a time, like a microwave or coffee maker.

Don’t recall if I posted this before, but we can see a generator in background, suggesting battery is used for convenience without need to discharge deeply.


DD588E84-067A-44C8-9040-43479139B5CD.jpeg
 

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8D battery weight is not an issue. You install it one time and if charged properly it will last 8-10 years. Just might need help with another person every 10 years. I actually bought the battery and put it in my pickup bed and then put a plank between the pickup bed and the van floor and slid the battery from one vehicle to the other. At the time I was 76 years old so no lifting. Helps that the battery was installed inside the van on the floor instead of under the van floor.
 

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Are RV builders really dangling batteries like that below the chassis?

Pretty sure I'd knock one off accidentally on my first visit into the dirt.
 

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Are RV builders really dangling batteries like that below the chassis?

Pretty sure I'd knock one off accidentally on my first visit into the dirt.
The battery wasn’t any where as bad as the generator. I took picture looking down at an angle, so it’s partly an optical illusion.

Looking at entire picture, you’ll see a little better that generator right behind rear axle of Extended ProMaster is as low or lower than axle. That's about 6” off payment.

By comparison, the battery was much higher off ground — although it sits back closer to rear bumper which reduces departure angle. Wish I had better picture.

D40AD1CB-FB7B-467C-A535-3BDF35E7D09C.jpeg
 

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Discussion Starter #29
Thanks for all the responses.....sounds like the larger inverter is the way to go and to turn it off when not using it!
 

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Thanks for all the responses.....sounds like the larger inverter is the way to go and to turn it off when not using it!
Sorry the thread has gone far from your original post :)

But since there're so many battery experts present, may I ask this question: If I'm not using my camper for a month, is it better to fully charge the house AGM batteries and then disconnect them, or just let the solar panel / MPPT controller float charge them everyday? Thanks.
 

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Sorry the thread has gone far from your original post :)

But since there're so many battery experts present, may I ask this question: If I'm not using my camper for a month, is it better to fully charge the house AGM batteries and then disconnect them, or just let the solar panel / MPPT controller float charge them everyday? Thanks.
I'm no battery expert but I can tell you that a standalone battery will self discharge, which isn't a good thing over time.
 

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Sorry the thread has gone far from your original post :)

But since there're so many battery experts present, may I ask this question: If I'm not using my camper for a month, is it better to fully charge the house AGM batteries and then disconnect them, or just let the solar panel / MPPT controller float charge them everyday? Thanks.
Let the solar panel do it. Remember, you also have a starting battery. That one is probably more susceptible because of the constant loads from vehicle computers. That needs to be kept charged as well. It doesn't take much to keep a charged battery charged, but depending upon how things are wired, your solar may or may not keep both house battery and starting battery fully charged.
 

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what's the consensus on constant trickle charging vs full charge and disconnect regarding battery life for battery banks that are unused for weeks or months at a time? The old school of thought was that batteries only had so many charging cycles, and the constant charging reduced their lifespan.
 

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what's the consensus on constant trickle charging vs full charge and disconnect regarding battery life for battery banks that are unused for weeks or months at a time? The old school of thought was that batteries only had so many charging cycles, and the constant charging reduced their lifespan.
Well, "constant trickle charging" is never a good idea. What you want is a "battery maintainer." This is not the same as the old school "trickle charger." A battery maintainer will add enough current to keep the batteries at their ideal float voltage, using voltage sensing circuitry. A trickle charger will just continuously feed a small amount of power to the battery, with no regard to battery voltage. This is bad. A battery maintainer will, of course, require plugging in to shore power.

A proper solar charging system will act as a battery maintainer once the batteries are full. With regards to battery life specifically, it would be better to have the batteries on a proper battery maintainer (or solar charging system) because if you disconnect the batteries, they will begin to self discharge. When you hook them back up, they will be exercised in recharging, using up some of their cycle life. But that is really a minor issue, not even worthy of consideration IMO. The issues that really matter (and the ones that tip the scale in favor of the battery maintainer approach) are:

1) if you disconnect them, there is always the possibility that they won't get hooked back up to a charger before they are catastrophically discharged

2) disconnecting and reconnecting the batteries is a pain, and if the batteries use the old lead squeeze-the-post type of connector, those connectors are not that robust and can eventually provide s substandard high current connection.

3) disconnecting and reconnecting the batteries might mess with the vehicles computers, causing certain setting to be lost (example: clock)

A proper solar charging system (or proper battery maintainer if parked inside) are the clear winners.
 

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Just to add a wrinkle. Because you are asking specifically about effect on battery life, I should mention that the ideal for lithium batteries in storage is that they not be fully charged. You would have to consult your battery manufacturer for specifics for your battery. It might be something like 40% charge is ideal. But whatever it is, it will also be dependent upon temperature. Here is some reference material.The bottom line is the same. The best thing you can do is have them "maintained" just as they would be in an off-grid solar home, because trying to meet the theoretical best case scenario for state of charge and temperature will drive you crazy. And look at the specs on this battery. You will see that they have an incredible number of cycles, as long as they are treated properly.
 
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