Battery power - how low can I go?

AJMike · 04-08-2020, 10:31 AM

Like most things it seems that the more I learn about something the more complex it seems and the less I realize that I really know.

In addition to asking questions on this forum about alternatives I have also spoken with some reps at some battery manufacturers - Battle Born for Lithium, Lifeline for AGMs and some local solar installers. Each, of course, is positive about what they sell or install so I have been trying to understand what is best for me in how I use my RV.

My basic problem is that the compressor refrigerator in the Winnebago Fuse eats power all night and when that is combined with the DVD player and small TV which my wife likes to watch before bed (when there is no sunlight for the solar panels) means that a full battery with 12.6v ends up at 11.9 - 12.1v in the morning. I thought I knew what that was - 50%, but the tech at Lifeline told me that 10.5v was dead, 12.6v was 100% full and 11.5-11.6v was 50%, so I am confused. Am I damaging my AGMs (65AH Interstate Group 34M)? Or not?

What voltage corresponds to 50% power in AGMs? Is the relationship between voltage and power linear? That is, if 10.5v is dead and 12.6v is full, is 11.5v 50% power? Or is that so low that it will damage my batteries? How low can I draw AGM batteries down?

The same question for Lithium. How low can I draw those down safely? I know they say 90% but BB told me that Lithium batteries automatically shut down at 90% so that seems to say that 90% is too much of a draw down. And one other question about Lithium - the BB batteries operate at 14.4v, not 12.8. Is that voltage not too high for the inverter and the resulting AC output?

Or am I just over-thinking this, as usual?

NOTE:

This post accidentally got appended to another thread. It was meant to be a separate thread and I will try to delete it from the other thread. Sorry for any confusion.

__________________

DavidM · 04-08-2020, 10:59 AM

Here is what I know and what I have read:

What I know is based on living aboard a boat with generic FLA (flooded cell lead acid) golf cart batteries with solar panels and a high output alternator on my engine to recharge them. I also had an accurate battery monitor that measures actual amp hours used.

Voltage is a very imperfect measure of battery state of charge. My battery monitor could be showing 50% SOC and the voltmeter would be showing 11.8 volts because I was drawing 10 amps at the time. If I reduced draw to zero the voltage would slowly rise and may ultimately have reached 12.1 or so but after several hours.

So if a battery is at a real 50% SOC the voltmeter could be showing 11.8-12.1 volts depending on the current draw. So only use the voltmeter reading after letting the battery rest for several hours. Even then I suspect you will find a variation of a few tenths of a volt at 50% SOC among different batteries.

What I have read:

AGMs have similar voltage vs SOC curves as FLAs and a similar reduction in voltage with current draws.

Neither FLA or AGM batteries should be routinely discharged below 50% SOC.

Lithium batteries have a very flat voltage vs SOC curve and voltage cannot be used to infer SOC.

BBs turn off at 10% SOC to protect the batteries but you can routinely use them down to the cutoff point with no harm.

And this is from physics tempered with experience: You can operate most DC appliances, inverters, etc at 14+ volts with no harm.

David

**creativepart** · 04-08-2020, 12:01 PM

It's generally accepted that 12.7v is full charge
12.1v or 12.2 volts is 50%
and 11.8 is dead.

BUT... there are always buts. Has the battery been at total rest long enough? What's the temperature of the battery? Exactly what type FLA, AGM, LiPo?

Your description of waking at 12.1v sound right. I think it was mentioned in another thread. You are just barely being well served by your battery bank. Adding more amp hours in larger batteries of any kind will just help extend that. Though keep in mind they may take longer to fully recharge to 12.7v because that need to have more power added.

Some battery manufacturers like to give their batteries a marketing advantage by claiming that you can take them lower than 50%. But the truth is you can take any battery lower than 50%. What you don't know is exactly how many times you can do that without damaging the battery.

Form what you have described I think your decision to replace your sub-par Group 24 FLA batteries with Group 31 100ah AGMs sounds well reasoned and well thought out.

If money was not an issue LiPo batteries would be ideal - but when is money not an issue?

What ever way you chose to go, I hope you'll install a shunt and battery monitor kit. It's time to stop trying to use the volts shown on your RV's monitor system.

https://www.youtube.com/watch?v=tV055vmZgvY

al1florida · 04-08-2020, 05:06 PM

Here is some great, fairly detailed info about RV Elect, batteries, charging, solar, etc.

These two link should help answer a lot of your puzzlement's.

The 12volt Side of Life (Part 1)

And part 2 of the above link
The 12volt Side of Life Part 2

AJMike · 04-09-2020, 02:59 PM

Quote:

Originally Posted by creativepart

https://www.youtube.com/watch?v=tV055vmZgvY

Watched this, Thank you for the link. I have ordered this and should get it installed next week.

I am assuming that the information from the monitor will help me understand what my usage is and so what I will need to keep stuff running.

al1florida · 04-10-2020, 04:46 AM

Quote:

Originally Posted by AJMike

Watched this, Thank you for the link. I have ordered this and should get it installed next week.

I am assuming that the information from the monitor will help me understand what my usage is and so what I will need to keep stuff running.

Exactly. Knowing how many AH (Amp Hours) you have used and just as important (actually in my experience more important) how many AH you have put back in the battery.

Be sure to go the first link I gave earlier The 12volt Side of Life (Part 1) and scroll down to these sections:
-- Care of your batteries
-- Charging your batteries
-- Converters vs real battery chargers

Understanding the above info is key to using and maintaining your batteries.

With the battery monitor installed you will know the status of your battery charge and usage. Reading the details in the link will help understand just why it is important to have the monitor.

A key thing to keep in mind, is that it takes some planning and monitoring to get your batteries recharged after using them. Lead acid batteries don't just get recharged in a couple of hours of charging. Much more detail in the section "charging your batteries".

DavidM · 04-10-2020, 06:01 AM

I skimmed through the two articles referenced above. They were mostly ok, with a few inaccuracies, but woefully out of date. Here are some quick comments:

1. Indicates you shouldn't charge more than .1 C or ten percent of your battery's capacity. Most golf cart deep cycle manufacturer's say .2C is ok and some AGM manufacturers say .3C is ok. I have used .25C for years with GC batteries and experienced no capacity degradation.

2. The discussion of converters being fixed voltage is accurate but only for 20+ year old RVs. Modern RVs are delivered with three step converters, or should we say chargers. Converters was an old term probably used to indicate a fixed voltage and for RVs continuously plugged into shore power. The converter "converts" shore power to use for DC loads.

3. No discussion of Firefly or Lithium batteries. These have become the preferred solutions for higher capacity and faster charging.

David

**creativepart** · 04-10-2020, 07:42 AM

Quote:

No discussion of Firefly or Lithium batteries. These have become the preferred solutions for higher capacity and faster charging.

David, I don’t mean to be picky or harsh, honest. But you keep lumping “Firefly” batteries in equally with Lithium as if those are the two choices that RVers make. I know you base this on them being a possible choice on boats, but as discussed previously these are unheard of in RVing.

I bring this up because it’s confusing to folks new to this topic to make this statement.

There are probably a few other battery types that “could” be a choice for RVers. But because they are not a common option they simply are not included in the general discussion as you are doing with this boat battery.

DavidM · 04-10-2020, 09:04 AM

I totally disagree with your characterization of the Firefly battery as strictly a boat battery. Just because the RV community doesn't know of or talk about them doesn't mean that they are bad or inferior to Li batteries.

Here is a link to a post I made on a boating forum comparing all of the prevalent battery types. Firefly's are about as cheap as AGMs on a $/usable amp hour basis and require no special charger to use fully unlike Lithium batteries.

See: https://www.trawlerforum.com/forums/...tml#post866118

David

Goodspike · 04-10-2020, 10:26 AM

Reading through this thread explains a lot of the consumer reviews on deep cycle batteries where the complaint is short life span.

**creativepart** · 04-10-2020, 10:47 AM

David,
That thread you linked to on the boat forum says that you're thinking of buying an RV. So, you don't have any experience with the battery in an RV that you can add. Correct?

I did a search and found dozens of boating references for the battery but only a couple RV discussions from a few years back. But no recent discussions and certainly no reports of how this is working out in an RV.

That's my point - discussion on current RV Battery choices don't really include Microcell Carbon Foam AGM batteries or the Firely brand name. Maybe that will change in the future, but in the 4 or more years the battery has been on the market this has not happened.

DavidM · 04-10-2020, 12:27 PM

First let me say that I have no financial interest in Firefly batteries. I would like to get the word out that Firefly batteries are another option for RVers to consider.

Even though I do not currently own an MH, but I do have a nice camping trailer that uses 10 amp hours on average each day. But I do have thirty years of boating experience where I used 75 amp hours each day for mostly powering a DC refrigerator.

New RVs are being delivered with DC refrigerators now. So what had been a minor problem of 10-30 amp hours daily use with an absorption fridge has now skyrocketed to 75+ amp hours to power the DC fridge. So bigger solar systems and conversion to LPO batteries are being installed in addition to converter upgrades and B2B chassis alternator charging.

I want to point out that the Firefly is an intermediate solution between the standard OEM batteries and whole hog conversion to LPO batteries. You can get 1.6 times the usable amphours from the same battery size at half the cost of LPOs.

Firefly is a new company and production is limited. So I am sure that they are focusing their marketing on the boat market. The RV market will come along in due course if RVers find them useful.

David

al1florida · 04-10-2020, 03:28 PM

Quote:

Originally Posted by DavidM

I skimmed through the two articles referenced above. They were mostly ok, with a few inaccuracies, but woefully out of date. Here are some quick comments:

1. Indicates you shouldn't charge more than .1 C or ten percent of your battery's capacity. Most golf cart deep cycle manufacturer's say .2C is ok and some AGM manufacturers say .3C is ok. I have used .25C for years with GC batteries and experienced no capacity degradation.

2. The discussion of converters being fixed voltage is accurate but only for 20+ year old RVs. Modern RVs are delivered with three step converters, or should we say chargers. Converters was an old term probably used to indicate a fixed voltage and for RVs continuously plugged into shore power. The converter "converts" shore power to use for DC loads.

3. No discussion of Firefly or Lithium batteries. These have become the preferred solutions for higher capacity and faster charging.

David

If you know of a website that has updated info and with much of the same basic detail about RV 12V electrical systems, batteries, charging, some solar info, 12V power consumption examples, please pass it on. I would love to find one to recommend to folks who need basic detail.

For example the OP in this thread is getting different info from different sources about what battery voltage shows what the SOC of his battery bank is.

The links I gave earlier, provide very good basic detail. Much, much better detail than I can give in a few or several paragraphs in a forum posting.

I agree some of the info is outdated, however the basics are there.

I also agree that charging at 0.1C is very low for golf cart type batteries. I have always use about a 0.25C charging rate when I still had lead acid batteries.

I do question your statement: "Modern RVs are delivered with three step converters, or should we say chargers" . I would be surprised to find entry level Class C and Class A motorhomes, and vacation quality travel trailers have 3 stage chargers. Many times the folks that buy these RV's are the same folks wanted to spend a few days dry camping/boondocking and want to know more about charging their batteries. I have to admit, I have not spent any time checking out this type of RV at RV shows or reading the owners manuals to see if they really do have 3 stage chargers.

Lithium battery info would be nice. However even with the "drop in" lithium batteries there are cautions and directions from the selling companies about just how to use the batteries and set up the proper charging parameters. That level of detail is usually beyond the knowledge of people needing basic RV electrical info.

I would love to find a website with lithium battery detail similar to the website I gave earlier.

DavidM · 04-10-2020, 05:52 PM

I too thought that all RVs came with simple, single voltage converter/chargers. I posted as much on the high tech Sprinter forum: Sprinter RV's & Conversions Talk, https://sprinter-source.com/forum/forumdisplay.php?f=5. They quickly corrected me. Evidently the Progressive Dynamics 9245, the ubiquitous converter on many new RVs is a three step charger. It won't charge LPO batteries to their full potential but the 9100LV series apparently does.

I guess I found the article you referenced out of date and since I know quite a bit about FLA batteries having lived aboard on the hook for several years, I thought it was a bit elementary as well. I realize that my elementary is another person's rocket science. I think the only way you can develop knowledge on the net is to read, question with an open mind tempered with science and read some more.

In that light here is an article on LPO batteries by a guy who does a lot of marine electronics work and sells Lithionics batteries: https://marinehowto.com/lifepo4-batteries-on-boats/. I can't begin to endorse it as being correct, just an article from someone who seems to understand LPOs. It is long and rambling but lots of info (well maybe opinions) in there.

David

**creativepart** · 04-10-2020, 07:15 PM

Quote:

Originally Posted by DavidM

In that light here is an article on LPO batteries by a guy who does a lot of marine electronics work and sells Lithionics batteries:

Perhaps a couple of RV Lithium articles would be helpful, too:

https://amsolar.com/diy-rv-solar-ins...ns/edbatteries

https://www.fateunbound.com/lithium-vs-lead-acid/

https://www.technomadia.com/2011/10/...cid-downsides/

https://www.technomadia.com/2012/09/...-rv-batteries/

https://www.technomadia.com/2011/11/...-battery-cost/

MicroMinnie · 04-10-2020, 07:57 PM

For what it’s worth, the WF8900 power center that sits in a ton of RV’s including our Minnie 2018FBS is NOT compatible as delivered from winnebago with Lithium batteries.

However, there is a circuit board replacement as a direct drop in (Around $200) to output DC voltage suitable for charging LPO batteries. here’s the replacement partnumbers to make it work

WF9850L2 is the complete Lithium unit
WF8959L2-MBA is the replacement mother board for all WF 8900 series power centres Lithium compatible

AJMike · 04-10-2020, 08:23 PM

Quote:

Originally Posted by MicroMinnie

For what it’s worth, the WF8900 power center that sits in a ton of RV’s including our Minnie 2018FBS is NOT compatible as delivered from winnebago with Lithium batteries.

What does this do? And where is this physically located in your RV? Is this what provides power to the batteries from shore power and/or the generator?

MicroMinnie · 04-10-2020, 08:58 PM

Yes part of that box has the battery charger, not sure if winnebago has an option on RV’s or Travel trailers for Lithium batteries from the factory. it they do the box would look the same but has a different charger baked in. the picture attached is what it looks like and has all the breakers in it as well.

You can spend thousands on new power systems, the sky’s the limit

al1florida · 04-16-2020, 04:51 AM

Quote:

Originally Posted by AJMike

What does this do? And where is this physically located in your RV? Is this what provides power to the batteries from shore power and/or the generator?

It is a converter/charger that is supposed to be designed for charging Lithium batteries.
I did an internet search and here is a link to the MFG website with details about the converter. Take a look at the specification section and also down the manual for the converter. Lots of very good info in the manual.
https://wfcoelectronics.com/product/wf-9850l2/

If you haven't read this link that Creativepart gave from AM Solar, it is well worth reading.
https://amsolar.com/diy-rv-solar-ins...ns/edbatteries

Be sure to watch the video at the end of the above article about lead acid battery charging.

Additionally there are a lot more very good instructional articles at AM Solar. Just click on the list of articles at the left hand side of the article at the beginning of the article.

Also the article I referenced earlier has lots of good info: The 12volt Side of Life (Part 1)

Lefler39 · 04-16-2020, 10:44 AM

My 2 cents as a 2018 Winnebago Navion owner

I have the orginal group 24 (2) NAPA 8240N lead acid 75 AH batteries installed by Winnebago. Battery compartment is in my cabin step. Circuits are 30 AMP.

As you stated, I have similar concerns about operating my RV during nightime hours.
Hunkering down for the evening, I have a Microwave for popcorn, Gas furnace with fan if needed, Compressor Refrigerator and DVD or local TV for watching

Winnebago Cabin Battery Display is strictly a voltage meter and is behind a cabinet door.

I just installed a AiLi Volmeter next to battery step that mimics a fuel guage for these cabin batteries to display its charge usage. The nice thing is you program their voltage, AH and it will display a gauge register 100% and you can immediately see and determine your nightime life expectancy as usage begins in the evening. It alarms you at or near 50% to turn off all devices. I have a ONAN propane generator as the backup charger to boost the batteries if needed.

https://www.rvhabit.com/post/install...itor-from-aili

Minimalistic Off Grid RV living has its challenges and can have costly upgrades for one to mimic On Grid living comforts in your RV.

I plan to remove and install (1) 100 AH Lithium group 31 for this small battery step bay. After learning what the AiLi results are once they lift our Corona Virus Lock down.