Dry Camping Battery Life

[n0mad]

Originally Posted by DeWat

As far as the 50% rule, isn't this why we have deep cycle batteries for the house? Aren't deep cycle batteries designed for deep discharge using a significant part of their capacity? I'm pretty sure that golf carts use deep cycle batteries (the same types we use for the house), is anyone saying that golf carts should not be run less than 50% of their capacity? Not arguing, but what's the point of a deep cycle battery if we're going to use it like an engine battery?

You can discharge them to 20%, but at the cost of lifespan. 50% is the rule of thumb/compromise to get the most life out of them.

Most starting batteries are only discharged a few percent, so you really should be comparing to 5% discharge. You aren't treating them at all like an engine battery when you are discharging them down to 50%.

Trojan publishes this chart which should help. 50% is the usual compromise.

[gpounder]

Originally Posted by DeWat

As far as the 50% rule, isn't this why we have deep cycle batteries for the house? Aren't deep cycle batteries designed for deep discharge using a significant part of their capacity? I'm pretty sure that golf carts use deep cycle batteries (the same types we use for the house), is anyone saying that golf carts should not be run less than 50% of their capacity? Not arguing, but what's the point of a deep cycle battery if we're going to use it like an engine battery?

It is hard to compare a golf cart to a RV, the use is very different.

But just as an RV is designed to provide power overnight a golf cart is designed to support use for the day on a golf course.

Remember the 50% idea give you a margin for reliability. As the battery ages or if you do not charge it up fully that 50% start to be really a higher number and when the battery is dead, you used 100%.

Same thing happens with a car battery, If I said typically you use only 10% to start your car and as the battery ages you finally have used all available power to 100% and now you have no margin and must replace it.

So if you use the RV to say 90% of capacity then in a short time the battery will no longer support your needs. That extra 50% reserve is what buys you time.

There is no chart for this, just logic.

[DeWat]

Originally Posted by n0arp

You can discharge them to 20%, but at the cost of lifespan. 50% is the rule of thumb/compromise to get the most life out of them.

Most starting batteries are only discharged a few percent, so you really should be comparing to 5% discharge. You aren't treating them at all like an engine battery when you are discharging them down to 50%.

Trojan publishes this chart which should help. 50% is the usual compromise. Attachment 283614

I understand the point being made by you and GPounder and the chart really helps, but even the chart shows the curve of life significantly shallowing right around 50%. Looking at that chart, I would guestimate somwhere between 300 & 500 cycle lifespan shorter for charging to 80% instead of stopping at 50%. That equals somewhere around 3-5 years shorter life span for the average, but active dry camper. If that's the case and since my batteries are still getting older everyday anyway (just like tires), it's a number I can live with. Kind of like why I drive my 6-8 mpg pusher to one-day events a couple hundred miles away (wedding & funerals) for the comfort rather than drive my 20+ mpg daily driver. Is my part about the lifespan flawed?

[n0mad]

Originally Posted by DeWat

I understand the point being made by you and GPounder and the chart really helps, but even the chart shows the curve of life significantly shallowing right around 50%. Looking at that chart, I would guestimate somwhere between 300 & 500 cycle lifespan shorter for charging to 80% instead of stopping at 50%. That equals somewhere around 3-5 years shorter life span for the average, but active dry camper. If that's the case and since my batteries are still getting older everyday anyway (just like tires), it's a number I can live with. Kind of like why I drive my 6-8 mpg pusher to one-day events a couple hundred miles away (wedding & funerals) for the comfort rather than drive my 20+ mpg daily driver. Is my part about the lifespan flawed?

In my personal experience, which isn't with Trojan brand batteries, the curve is a bit steeper. I suspect they are painting an somewhat optimistic picture with that chart.

If you're a full-timer and primarily boondock, you are running 300+ cycles per year. Looks to me like you get roughly 1200 cycles at 50%, but 750 at 80% DoD. You're losing another 37.5% of battery capacity, or going from a lifespan of four years to a little over two. Anecdotal, but they seem to have difficulty dealing with high discharge rates the older they get, especially after being cycled deeply, and you'll see the associated symptoms start well before they refuse to hold a charge (inverters shutting down due to low-voltage cutoff under load, etc).

I personally consider Lead Acid batteries to be junk and would just use them how you want, and replace them with LiFePO4 when they begin to cause you frustration.

[Winemaker2]

50% is easy to remember but IMO is a VERY conservative margin of safety.

Here is what Battery University has to say about this very topic - I modified my Myth Buster write-up to better agree with BU thoughts and included this as a reference.



From Battery University
BU-504 How To Verify Sufficient Battery Capacity
Figure 1 illustrates the breakdown of a battery that includes capacity fade and spare capacity. Adding 20 percent for fade and 20 percent for spare as a safety net leaves only 60 percent for the actual capacity.
Such a generous allowance may not be practical in all cases.

[Jon_C]

Originally Posted by Gary.Jones

No, I never try to run any of the AC units off of battery alone and don't know that you can. If you have DW and kids further behind the pilot and co-pilot seats, then you are right, you are going to need to run the generator to keep that area reasonable. You have a huge 12 volt alternator being turned by the Cummins, but that is not enough "juice" to run a roof AC unit in the Louisiana or Texas (or anywhere for that matter) August. Now, there are just the two of us so we can get by on the dash AC only in most months but not August or most of July. In those months, even with just the two of us in the front two seats, the dash AC is not enough and in that case, the Onan is always purring a few minutes before we turn one or two of those (no sense trying to Air Condition the back third of the Coach.... the Cummins always wins).

Oh, and yes, you have an Automatic Generator Start system on your coach that works very well. You get to set the AGS start voltage either in the Onan EC-30 control panel or the Vegatouch software/system depending on year and model of your coach.

Gary

I run my a/c while driving on a 340 amp alternator that replaced the stock 160 amp. Also a 5kw inverter. Works great even down here in TX. Bought the new alt from amazon.

My batteries will run a/c for 2 hrs. And i ran 4/0 cables to handle the DC load. So its possible...

[Smitty77]

I agree, for many owners just getting a few setting set, and if wet cell checking the battery periodically - supports their desired usage of a battery bank!

I also feel the posts on this thread, and few thousand more over the years, do show that many owners really like to get more involved in with the usage of their battery banks. (Some because they have to for remaining 'off grid' for extended periods. Others, well because they want to!).

As with many thing in RV'ing many choices available... and one approach does not fit all of us...

Best to all,
Smitty

[AnotherMike]

Originally Posted by richard5933

For comparison's sake, we have 780Ah of battery power (four L16). Our fridge is a 12vdc compressor fridge, and our furnace is an old school 30,000 btu propane unit with a 12vdc blower. All our lights are LED.

With fully charged batteries, we can dry camp for 2-3 days in cold weather, longer if we put out our portable solar panels. We only run the inverter if we want to watch a movie or TV.

One huge difference is that I use a small single burner portable propane stove to make coffee. Things like a Kureg just burn up way too much electricity to justify their use. I believe that there are non-electric machines for K-cups now as well.

Richard: this is NOT directed at you, just a general info posting...

A couple of other power saving tricks:

1) There are 12v TVs (i.e. does not require having an inverter) I have a Visio 22 inch that is 12v directly (model M220MV) that I picked up for under $100. It also works just fine as a monitor for my laptop (VGA 1920x1080). It came with a 12v @ 5 amp wall wart that sits in a drawer. I purchased a matching DC connector for the back of the TV and made up a power cord with a 5 amp automotive fuse in line.

2) Modern inverters are very efficient, but for the same efficiency factor a large inverter (1kw, 2kw, etc) will waste more power than a small one (200, 300, 500w) due to unavoidable conversion losses. If you are going to run your residential fridge 24x7 then it makes sense to have a dedicated small inverter just for the fridge... size it for 10%-15% more than the fridge requires when starting. This way you can shut down the big inverter(s) when not needed. Plus, having a dedicated inverter also lets the main act as a backup for the dedicated fridge small one in case the small one dies.

And if I'm on battery before I go to bed I move the a 1 gallon plastic milk jug from the freezer to the fridge section and then shut the fridge inverter off. In the morning I turn it back on and move the milk jug back to the freezer section (it is still quite frozen). That trick saves me 7-8 hours of battery drain. Just don't open the door at night!

3) Do not run an inverter to operate a cellphone charger. You are inverting 12vDC to 120vAC (with conversion losses) and then converting 120vAC to low voltage DC (with additional conversion losses). Just get an automobile (12vDC) cellphone charger (has only one level of losses).

4) If you use a CPAP it may make sense to search out one that runs on 12v directly. They do exist. My Airsense 10 is a 24v device and comes with a 120vAC to 24vDC (at 4 amps!) power brick. That's 100 watts! I made up a 12vDC to 24vDC inverter (less than $50) that has only one level of conversion losses and avoids having to run run the main inverter all night. And when I need to replace the Airsense 10 the new one will definitely be a 12v device.

Mike

[AnotherMike]

Originally Posted by Grenier

Is there a good introduction to battery life and electricity for motorhomes someone can direct me to?

http: // The 12volt Side of Life (Part 1) By Mark S. Nemeth

http: // The 12volt Side of Life Part 2

I made PDFs of both sections for my "RV" directory on my laptop.

When you get interested in solar then there is a lot more reading to do... starting with this:
https: // handybobsolar.wordpress.com

It may take you several evenings to read all of it, and then you will find yourself going back and re-reading it... and re-reading it... and each time discovering stuff you missed on the first read-through.

Mike

[n0mad]

You can do as little, or as much, as you want to on battery power. It's a matter of deciding what your goals are and building the appropriate bank.

Some people are happy with 12V appliances and running everything possible on propane, others want the FHU experience when unplugged. There are tons of possibilities between the two.

[richard5933]

Originally Posted by DeWat

As far as the 50% rule, isn't this why we have deep cycle batteries for the house? Aren't deep cycle batteries designed for deep discharge using a significant part of their capacity? I'm pretty sure that golf carts use deep cycle batteries (the same types we use for the house), is anyone saying that golf carts should not be run less than 50% of their capacity? Not arguing, but what's the point of a deep cycle battery if we're going to use it like an engine battery?

Something else related to how far down you run the batteries that doesn't always get considered is voltage level. Other than with lithium batteries, the further you run batteries down the lower the voltage goes. At a certain point the voltage gets low enough that not every device will run properly or without damage. Also, the lower the voltage the higher the amps. This means that wiring which may be perfectly fine at 12.5 volts dc are causing more voltage loss once than is acceptable once the voltage drops.

You can run your batteries below 50% SOC, but the voltage will drop and you may encounter problems aside from shorter battery life.

[AKOne]

Originally Posted by gpounder

For those of you reading this thread and thinking this is too much, let me offer a couple ways to simplify operations.

Managing your battery set does not have to be complicated. For most everyone normal use of the RV overnight on batteries is not a problem. The battery set should be big enough to do everything you need.

All you need to do is run the generator each day to the point your meter shows the batteries are charged and your good to go for another night.

Battery life depends mostly on keeping them watered for flooded batteries and not letting them sit for weeks in a discharged state.

That's it.

All the talk about 50% or 75% requires you to have a good understanding of battery systems AND have a way to measure actual consumption. When you know what your doing then getting more from the batteries is very possible.

Well said gponder! I only have 4 T105s that will run the frig all night after watching TV, running lights and maybe a hair dryer that evening. Run the generator the next morning until battery charge reaches float. After a couple years I have a pretty good feel as to what these batteries can handle. And, someday I will upgrade since we like boondocking.

[ldfeat]

A battery that reads 12 volts is about 50% charged: https://electronics.stackexchange.co...rge-percentage

[ldfeat]

A battery that reads 12 volts is about 50% charged: https://electronics.stackexchange.co...rge-percentage