Let's talk RV batteries

[Rubes]

Okay, I consider myself to be an educated man, but there is something about car/RV batteries that I just can't process in my brain. I have a small camper trailer that we like to take out several times a year, mostly to places without any hookups, so we rely on the battery a good portion of the time. I've been using a marine battery with it for some time, but I've had such a hard time managing it from year to year. Basically, I'm the kind of person who would only get maybe 2 years out of a battery before it died out, and it was frustrating.

 

The last couple of years, I've done better. I started removing the battery in between trips, got a trickle charger for the winter months, and installed a battery monitor in the camper so I could keep an eye on it. I also bought a set of portable solar panels, which I have to say is one of the best investments I've made. So easy to use, and they provide a level of security on longer trips knowing that I'll be able to keep the battery charged. I've had my current marine battery for at least 3 years now and this system seems to be keeping it in good shape, even though I truly don't know what the hell I'm doing.

 

I'm interested to hear what others' experiences are with RV/camper batteries and what solutions you've come up with to keep them working and reliable.

 

I'm also interested in getting a better sense of how to use the battery monitor readings to assess the battery itself. For instance, attached here is an image I got online to interpret voltage reading and battery state of charge. My understanding of car/marine batteries is that you don't want the battery state to fall below 50% or you start to see degradation of the battery, is that correct? So is the idea then that when you see a voltage at or below 12.4 on the monitor then that's an indication that the battery state is falling below 50%?

 

 

Does it matter when that reading is taken, or what the demand on the battery is at that time? In other words, are you supposed to get an idea of the battery state when the battery is not hooked up to any other source (car or solar panels) and there are no pulls on the battery (ie, no lights or other electric devices being used)? Or does the state of charge apply no matter what the battery is supporting, and you don't want the voltage to drop below 12.40 at any time and with any usage? So if I'm out on a trip and I have the lights on and a fan plugged in or whatever, and the meter shows a voltage of 12.30, I should shut some things off to protect the battery?

 

I don't know what my block is, but for some reason I can't keep this stuff straight. Infectious disease epidemiology, no problem. RV battery...I'm screwed.

 

[PolishDave]

2 hours ago, Rubes said:

My understanding of car/marine batteries is that you don't want the battery state to fall below 50% or you start to see degradation of the battery, is that correct? So is the idea then that when you see a voltage at or below 12.4 on the monitor then that's an indication that the battery state is falling below 50%?

 

I am no expert.  So take my advice for what it is worth.

 

I do run solar panels and an off-grid batteries + inverter system.

 

Your understanding is correct that you don't want to draw lead acid batteries down below 50% because you can damage the battery and drastically shorten its life.

 

Yes 12.4v = maximum discharge before running the risk of really shortening battery life.

 

2 hours ago, Rubes said:

Does it matter when that reading is taken, or what the demand on the battery is at that time? In other words, are you supposed to get an idea of the battery state when the battery is not hooked up to any other source (car or solar panels) and there are no pulls on the battery (ie, no lights or other electric devices being used)? Or does the state of charge apply no matter what the battery is supporting, and you don't want the voltage to drop below 12.40 at any time and with any usage? So if I'm out on a trip and I have the lights on and a fan plugged in or whatever, and the meter shows a voltage of 12.30, I should shut some things off to protect the battery?

 

You will experience a voltage drop when the battery is under load.   So a disconnected battery will typically measure higher voltage than a battery that currently has a draw on it.   The amount of voltage drop is affected by how much current you are drawing.

 

With a full charge on the battery, if you turn your lights on and plug in your fan, do you see an immediate drop from 12.8v to 12.3v?    If you do, then you probably need to decrease the load or add an additional battery in parallel because you are drawing too much current.   That way you could draw from both batteries at the same time.

 

You don't want to go under that 12.4 whether the battery is under load or not if that is the manufacturer's recommendation.

 

If you are getting a large drop under a small load, that is a sign that your battery is on its way out.  But it is relative of course.  

Edited September 16, 2021 by PolishDave

[Rubes]

14 minutes ago, PolishDave said:

You will experience a voltage drop when the battery is under load.   So a disconnected battery will typically measure higher voltage than a battery that currently has a draw on it.   The amount of voltage drop is affected by how much current you are drawing.

 

With a full charge on the battery, if you turn your lights on and plug in your fan, do you see an immediate drop from 12.8v to 12.3v?    If you do, then you probably need to decrease the load or add an additional battery in parallel because you are drawing too much current.   That way you could draw from both batteries at the same time.

 

You don't want to go under that 12.4 whether the battery is under load or not if that is the manufacturer's recommendation.

 

If you are getting a large drop under a small load, that is a sign that your battery is on its way out.  But it is relative of course.  

 

Thanks, @PolishDave. Just to clarify, I haven't seen the voltage drop below 12.4 yet, I was just using that as an example. Typically, the battery without any load will be somewhere between 12.7 and 12.8, and when using lights and such I'll see it drop to between 12.5 and 12.7 depending on how much load is being used.

 

We have a pretty small camper, so there's really only room (and need) for one battery. I've been considering switching to one of those expensive lithium batteries, where you don't have to worry about drawing it down even all the way to 0%. But then I'd probably have to get a lock for the battery box...

 

[aristocrat]

2 hours ago, Rubes said:

 

Thanks, @PolishDave. Just to clarify, I haven't seen the voltage drop below 12.4 yet, I was just using that as an example. Typically, the battery without any load will be somewhere between 12.7 and 12.8, and when using lights and such I'll see it drop to between 12.5 and 12.7 depending on how much load is being used.

 

We have a pretty small camper, so there's really only room (and need) for one battery. I've been considering switching to one of those expensive lithium batteries, where you don't have to worry about drawing it down even all the way to 0%. But then I'd probably have to get a lock for the battery box...

 

get a lithium battery. It’s not even a question.I’ve got them in my rv. I run a predator 3500 inverter generator which is so quiet it’s not even funny but you wouldn’t need one that big for yours.  I’ve got a Durango gold 382 mbq fifth wheel and we live in full time. Let me know if you need any help and I can also point you to some Facebook groups that can help as well 

[Rubes]

2 hours ago, aristocrat said:

get a lithium battery. It’s not even a question.I’ve got them in my rv. I run a predator 3500 inverter generator which is so quiet it’s not even funny but you wouldn’t need one that big for yours.  I’ve got a Durango gold 382 mbq fifth wheel and we live in full time. Let me know if you need any help and I can also point you to some Facebook groups that can help as well 

 

Thanks, I'm mostly waiting for the existing lead acid battery to wear out, then replace it with a lithium battery. We're so lightweight we don't have much need for a generator. Just mostly trying to get a sense of how to monitor battery wear and usage in a way that this brain can process. I like that with a lithium you don't have to be concerned about the battery state dropping below 50%...or to any % for that matter.

 

[WhoTom]

12 hours ago, Rubes said:

 

Thanks, I'm mostly waiting for the existing lead acid battery to wear out, then replace it with a lithium battery. We're so lightweight we don't have much need for a generator. Just mostly trying to get a sense of how to monitor battery wear and usage in a way that this brain can process. I like that with a lithium you don't have to be concerned about the battery state dropping below 50%...or to any % for that matter.

 

 

Try to keep it above 20% as a general rule. Frequently dropping below that will shorten its life.

 

 

[Rubes]

24 minutes ago, WhoTom said:

 

Try to keep it above 20% as a general rule. Frequently dropping below that will shorten its life.

 

 

 

Yeah, I would never push it like that, especially with the solar panels available.

 

[MarkyMannn]

Just FWIW, what I know from my Harley, between trips use a battery tender ALWAYS hooked up.  Not a charger, fries your battery