Dead Batteries- how bad?

[JoeC]

Originally Posted by danhannah

I don't know how a better battery monitor would have helped. I parked the rig with the inverter on, and left it for 5 days unattended. I guess a bluetooth type low battery alert system would have alerted me. Thanks!

Great question and I mean no offense in the next statement. It shows that many RVers don't really understand how their electrical system works; understandably so. Not everyone is trained in this area, including your typical RV service tech, and you should ask for professional assistance when making changes to the electrical system.

The shunt battery monitor not only can tell the observer the current state of battery charge but can and should be used to discover parasitic loads, quantify device loads and indicate how much load capacity actually exists in that battery bank vs what is printed on the side. But what does this all mean?

Parasitic loads are small "unknown" loads that constantly drain small amounts of battery power, 24/7 for whatever reason. Either eliminate them or understand them as a "xx amp hour load" per day. Example: Your inverter, when turned on, draws an amp or so without being used, no load at all, unless you turn it off when not in use.

Knowing exactly how many amps each appliance draws off the battery will tell you how many hours you can operated that appliance on one charge cycle. Amps times hours running equals amp hour (ah) load. Add them all up. A 5 amp (600 Watt) AC load through the inverter will be pulling about 53-58 amps from your battery. The reason why running an air conditioner off the inverter is not a good idea; they're 1,200 Watt or more.

The factory says that you have a 100ah (amp hour) capacity battery. It's printed on the battery, right? Well, maybe. You may actually have a little more with a brand new battery or much less with a used or abused battery. Take away 50% for lead acid batteries and 20% for lithium batteries and you are left with an approximate (50 lead acid, 80 lithium) amp hour capacity, in theory under ideal conditions. Now here's the beauty of the monitor. It knows about every little electron that left the battery and how long it's been discharging. It also knows the present voltage level, even under load. Voltage times current draw equals power (p=v*e). It tracks all this automatically. So, say, after 40ah of load (lead acid battery) you notice that your battery voltage is now below 12 volts, maybe 11.9, you're done. It's time to recharge and you have 40ah of actual capacity in your battery bank, not 50. Now you understand how many hours of living in the RV can be had on one charge cycle or how much capacity may be left for tomorrow.

By the way, with lead acid batteries, if you take out 50ah of power you have to put about 100ah back in to get back to full. That's a charge efficiency of around 50%. And if you only partially charge that battery, well, you just put another nick in its capacity and life expectancy. Lithium batteries charge at 90+% efficiency and are not injured by partial charging. In fact, if you operate many lithium batteries between 50 and 80 percent charge, they can last almost indefinitely. Most are built today to handle 3,000 or more complete charge cycles and lose only a small percentage, maybe 3%, of their power monthly when stored or not in use. Lead acid is more like 20% monthly loss in storage and require trickle charging.

Knowledge is power and battery monitors can give you the knowledge to take control (power) of your electrical system, instead of having it the other way around. I hope that I have been more helpful and informative than insulting with this post. Happy camping! After all, isn't this what it's all about?

[Topsail]

JoeC, now that is a solid write up. I'd like to learn more about the "shunt battery monitor". Maybe you could suggest some reading material and links for a decent kit.

I see an upgrade in my future.

Thanks

[Jaeger]

I had a similar battery depletion event, but with a one-year-old 12v group 31 deep cycle flooded lead acid battery. It's AH capacity was substantially reduced. I had left the master switch on and the constant one-plus amp drain completely drained the battery. I was able to charge it back up to full voltage and the battery tested "good" at a local battery shop. Based on that test, I went ahead and used it on a short trip, but over a few months, it became clear that the battery had been damaged and would rather quickly lose its charge.

This episode led me to invest in a Victron low-voltage battery disconnect. Now, if I forget to turn anything off, the disconnect will automatically open the circuit and prevent a damaging discharge.

[JoeC]

Originally Posted by Topsail

JoeC, now that is a solid write up. I'd like to learn more about the "shunt battery monitor". Maybe you could suggest some reading material and links for a decent kit.

I see an upgrade in my future.

Thanks

You may want to start with an internet search of "shunt battery monitors" for a general background "education". Get to know what they do and how they basically work. The search will likely bring up vendors and manufacturers of said products. Read their marketing material and take with a dose of salt. Remember "marketing" if code for stretching the truth to the point where it's about to break. Some go beyond that. It's not so much what they say, it's what they don't say; little left out tidbits that may cast shadows over their stellar product or accurately tell what their product really does. But at this point you are just trying to get a basic education on the topic.

Then research a few of the actual products and read their reviews (maybe another search). You will find several products over a pretty wide price range. Low end products tend to be missing something in the way of proven technology, reliability, customer service or support. Expensive products tend to offer more, have better reliability and support. Ask yourself: Do I need these added features? You may need more education to answer this question. Find out what others (hopefully knowledgeable) have done and used and get their reviews." You get what you pay for" is not really accurate, it's more like you get no more than what you pay for, meaning you can get less. So stick with reliable brand names unless you are very knowledgeable on the subject and know how to deal with the shortcomings.

For me, I chose Victron Energy. I didn't like that they are not a U.S. company but they were an early leader in the technology and were well received by their customers, plus had a huge array of electric components and interconnect technology used extensively in Europe. For whatever reason, the U.S. had very little in the way of this type of technology for the RV market. That was 3 years ago and time can change a lot of things.

Most of what I know today is from actually using the product and less from reading about it. But I also researched battery technology, solar panels and controllers, inverters, everything that I would be adding to my RV and making sure that they would all "play" well together. My advantage over many RVers is that I have a background in electrical and electronics plus a career working from a service engineer on up to technical design consultant. For me, learning "stuff" has been a life long journey.

There are three way to do things: The right way; the wrong way; and the way that works best for you. Operative word: "works". So learn and research as much as you can, ask others who have gone before you, and reach your own conclusion. Or, pay someone reputable to do all this work for you. But the trouble with many vendors is that they are very myopic and tend to offer one-size-fits-all solutions aligned with a fixed line of products. Not the best in all respects, but hopefully a proven working system.

Get to know your RV's entire electrical system backbone, know exactly what you want to accomplish with the modifications and check all of the specs with a trained engineer to be sure that all of the components, including the connecting wire, will work well together in all instances. Make one change to that design and you get to go back to square one, really. This stuff is not modeling clay. Every additional modification will need to be reviewed with the entire system to keep from shooting yourself in the foot. You could end up overloading a wire (fire hazard), overloading a component (early failure or incapable of working), overtaxing you battery bank or charging devices where you consume more energy in a day than can be put back during the next day. The list goes on.

My hope with this post is to convey the idea that RV electrical systems are complicated, get more complicated with modifications and users will need to seek additional education and qualified help when making changes to them.

Best wishes. Good luck and happy camping.

[creativepart]

Originally Posted by danhannah

I don't know how a better battery monitor would have helped. I parked the rig with the inverter on, and left it for 5 days unattended. I guess a bluetooth type low battery alert system would have alerted me. Thanks!

It would not have helped in your situation. A bluetooth device can only reach a couple dozen feet at most.

It happens. I know the 2nd time I put my RV in storage I forgot to hit the disconnect. The solar panel helped some, but I was still at 11.9v when I checked up on the RV a couple weeks later.

The batteries charged right back up and I'm going on 3 years in July. So, it wasn't catastrophic.

As to a shunt based battery monitor... it wouldn't have helped here but was probably one of the very best and easiest improvements to make on the motorhome. Definitely.

[al1florida]

Originally Posted by danhannah

I don't know how a better battery monitor would have helped. I parked the rig with the inverter on, and left it for 5 days unattended. I guess a bluetooth type low battery alert system would have alerted me. Thanks!

danhanna, I agree with your statement. Based on the the battery usage info you have provided, I don't think you have a "need" to install a battery monitor.

Others have give good, very detailed, info recommending battery monitor.

Additionally I am a very strong advocate for battery monitors: FOR RV'ers who dry camp or boondock more than just overnight once in a while.

In your case, battery voltage charts showing the % of discharge, do a reasonable estimate of the status of your battery.

NOTE: You must have most all loads turned off for the voltage to state of charge to give a good reading. A couple of lights being on is fine, but no heavy loads. Things running of an inverter need to be turned off.

[danhannah]

Good comments all.

Is this arithmetic correct? For the inverter in standby mode:

1 amp used X 24hrs X 5 days = 120 amp hours used

2 Trojan T105s = 250 amp hours (at 100 hour rate) divide by 2 = 125 amp hours available

So, with the parasite load of the inverter, expect the Trojans to last about 5 days.

Thanks again

[BobC]

Golf cart batteries are pretty tough. If you're concerned about their condition, you can take them to a battery shop and they can desulfate them. I had this done to a set that came with a boat I bought. They wouldn't hold a charge but were fine after the battery shop desulfated them.

[al1florida]

Originally Posted by danhannah

Good comments all.

Is this arithmetic correct? For the inverter in standby mode:

1 amp used X 24hrs X 5 days = 120 amp hours used

2 Trojan T105s = 250 amp hours (at 100 hour rate) divide by 2 = 125 amp hours available

So, with the parasite load of the inverter, expect the Trojans to last about 5 days.

Thanks again

The math is correct. However the battery discharge, IF the 1amp would be the only load, that would be 5 days to about 50% discharged. 50% discharge should be about the max discharge before recharging. 50% discharged is about a 12.0 to 12.1V "no load" reading. I consider no load to be less than about 5-8 amps when checking the battery voltage to estimate the state of charge.

As I remember you stated your battery voltage was down to about 10.4V which is 100% discharged (0% left in the battery).

There is most likely something more that was using power than just the inverter. The microwave keep alive stuff probably uses 1/4 to 1/2 amp of DC power thru the inverter. Some or many Winnebago motorhomes connect the gas/elect fridge's electric side to the inverter. So instead of the fridge (in auto mode) going to gas when off of shore power it pulls 15-30 amps of 12V DC through the inverter, if the inverter is on. This really aggravates me when I forget to switch my fridge to gas only and I look at my battery monitor 15-30 minutes later and see -27amps on the display. GRRRR

My experience with my last 4 RV's, there was a phantom load of 0.2 to 2 amps with the inverter OFF. I only knew this because I had battery monitors in the RV's. Before that I was flying blind, not knowing the status of my batteries.

In one of the RV's I had a 1000 watt Magnum inverter/charger and it pulled somewhat over 1 amp when turned on, as I remember. My current inverter/charger, a 2000 watt Magnum, pulls about 2 amps when turned on and no 120V AC load.