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Old 01-16-2021, 09:58 AM   #1
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2017 Interstate Grand Tour Ext
St Pete Beach , Florida
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Newer than Newbie - Battery Question

Hello to All,
We recently purchased a 2017 AI GT - basically as is where is so did not receive any sort of training.
I have a question about the coach battery usage.
We currently have it plugged into 20 amp shore power - batteries read 13.4 V
We will soon drive from Ont. Canada to FL and will want to sleep in our unit overnight during the trip.
Couple of questions,
Assuming only the fridge is running will our coach battery last the night?
How low can we drain the coach battery without hurting it.
Is there some sort of low batter warning device or will the fridge automatically turn off when the voltage gets too low protecting the batteries
Thanks for any guidance you can give
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Old 01-16-2021, 10:41 AM   #2
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Without knowing all your systems, you will likely have more background drain than just the fridge.I would run a small generator when stopped for night.At least to charge everything up, while you are using systems before going to sleep.
It is just way easier on any battery bank.
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Old 01-16-2021, 10:53 AM   #3
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Thanks for your comments
Our AI has a generator so yes we can/will top up the coach batteries before we turn in for the night
Can you comment on my low battery questions - I am somewhat paranoid that I will drain them too low?
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Old 01-16-2021, 11:23 AM   #4
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Originally Posted by 4DSX4 View Post
Thanks for your comments
Our AI has a generator so yes we can/will top up the coach batteries before we turn in for the night
Can you comment on my low battery questions - I am somewhat paranoid that I will drain them too low?
You should be. With nothing but a volt meter on your control panel, it can be challenging to accurately track the state of charge. There are plenty of charts out there that will tell you the approximate state of charge at a given voltage, but those charts only apply to healthy batteries.

If your batteries are original equipment, there's a good chance they are already damaged due to prior multiple draining events caused by the previous owner, and hold far less charge than one might expect.

It's not unusual to see Interstates gobble up the charge in their original batteries overnight while dry camping (e.g. no shore power). Usual drains include fridge, propane valve, propane heater fan, lights, and on and on. Without an amp meter telling you how much you're actually drawing at any moment in time, power draw is a difficult thing to manage. With standard equipment, Interstates are not particularly good when it comes to dry camping unless you're willing to run your noisy generator quite a bit - which guarantees any nearby neighbors would despise you.

While the generator will provide power when it's running, the idea that running it for an hour or two will "top off" lead acid batteries is a fallacy. If you have lithium batteries, that's definitely possible, but lead-acid batteries charge asymptotically over a long period and will not likely reach a full charge unless fed power for quite some time...such as all night, overnight, with a shore power input. If your system is working properly it's possible the alternator will help you with charging the coach batteries while driving, but unless you have an amp meter and can see how much power is actually being fed into the coach batteries as you drive, one should should proceed cautiously with that assumption.

As you probably know, the Canadian US border is closed to all but essential travel. Even if you are able get into the US in your van, getting back into Canada the same way may be quite a challenge. Before attempting, please do your homework and ensure you have all the right paperwork or you may find yourself unable to enter the US, or even more challenging, spending quite a bit more time in the US than you had anticipated.
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Old 01-16-2021, 11:30 AM   #5
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I would not trust voltage to tell you the state of charge. The batteries need to be sitting idle for several hours before the voltage means anything. One of the first things I did was add a battery monitor kit and upgraded the Magnum remote to give state of charge. If your batteries are at 100% and if you are truly only using the fridge, then you can probably make it through the night. I understand that the GT has separate fridge and freezer, and you may not make it when running both. You will likely get enough charge from the alternator when driving the next day to get your batteries back up to 80ish %, but you can't count on the driving or the stock solar panel to get your batteries to 100%. Your generator will also quickly (<1hr) take you 80ish% SOC if you have the Magnum charger set at a high charging rate. But you'll need to plug in for several hours sometime on day 2 to to get to full 100%. But getting to 80% on each subsequent day should prevent serious damage to the battery if it isn't below 40-50% each morning. Lifeline battery technical manual shows how long (how many discharge cycles) the battery will last at different draw-down levels.

Far as I am aware the only automatic battery cut-off protection is on the invertor - which you will not be needing to run the fridge.
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Old 01-16-2021, 11:38 AM   #6
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What kind of batteries do you have? Assuming the batteries are original they may be approaching the end of their useful life.
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Old 01-16-2021, 11:40 AM   #7
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Many thanks Rocinante
I fully agree - I am sure our coach batteries have been drained more than once already (were drained the day we picked it up)
Long story short - what is the min. voltage any coach batteries should be drained to? (need this info for when we replace the ones we have)
And I assume there is no sort of low voltage warning mechanism?
Thanks regarding the border
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Old 01-16-2021, 11:42 AM   #8
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Originally Posted by Titus View Post
I would not trust voltage to tell you the state of charge. The batteries need to be sitting idle for several hours before the voltage means anything. One of the first things I did was add a battery monitor kit and upgraded the Magnum remote to give state of charge. If your batteries are at 100% and if you are truly only using the fridge, then you can probably make it through the night. I understand that the GT has separate fridge and freezer, and you may not make it when running both. You will likely get enough charge from the alternator when driving the next day to get your batteries back up to 80ish %, but you can't count on the driving or the stock solar panel to get your batteries to 100%. Your generator will also quickly (<1hr) take you 80ish% SOC if you have the Magnum charger set at a high charging rate. But you'll need to plug in for several hours sometime on day 2 to to get to full 100%. But getting to 80% on each subsequent day should prevent serious damage to the battery if it isn't below 40-50% each morning. Lifeline battery technical manual shows how long (how many discharge cycles) the battery will last at different draw-down levels.

Far as I am aware the only automatic battery cut-off protection is on the invertor - which you will not be needing to run the fridge.
Great info Titus - thanks!!
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Old 01-16-2021, 11:43 AM   #9
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I would try not to let the voltage drop below 12. 12.5 is better.
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Old 01-16-2021, 12:41 PM   #10
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Regarding voltage and state of charge, there's a chart on this web page, below the Lithium chart. Again, this chart only applies to healthy lead acid batteries that, per Lumatic above, have been allowed to rest for a while.

Our batteries were so bad that they would drop from 13.4 to 12.4 volts if you even blinked while drawing just enough juice to keep the propane valve open. They're gone now, replaced with Lithium and an entirely new solar / charger / inverter system. We're not 100% done with the upgrade, chasing a gremlin that appears to be related to a possible transient DC ground fault somewhere in our system, but it works well enough and at this point we can confidently camp without shore power.

Whoops, almost forgot the link: https://batteryuniversity.com/learn/...tate_of_charge
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Old 01-17-2021, 10:33 AM   #11
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I mounted a GZ3000 behind the driver's seat. The plug for the fridge is in the cabinet and can be easily routed out. Do you see the hole for wiring under the folding table? When you stop driving for the day, plug the fridge into the GZ. The GZ will also power an electric blanket or a fan. While you are driving the next day, charge the GZ. You can now boondock in your Interstate without concerns over batteries. I'm here for questions.
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Old 01-17-2021, 11:37 AM   #12
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My 2020 Interstate has an automatic generator turn on when batteries reach a certain level. I can adjust the level. Since Covid I have been making frequent trips that require overnight stays at rest areas. Now being winter I use the heat. While it runs on propane, the fan uses the battery. During 10 trips, the generator automatically started twice in the early morning hours. Seems to do what was intended
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Old 01-17-2021, 12:52 PM   #13
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I would highly recommend unplugging in your driveway at night and checking your voltage in the morning just like you are going to when you are on your trip if you have time before you leave.

We have a Lounge, which has a different refrigerator setup than the GT, but we could go around 8 hours unplugged before things started to become concerning.

As someone else said, if your batteries go below 12.5 volts, they are starting to discharge enough to cause damage to the batteries.
One thing to keep in mind, if you run your house batteries too low, the generator wonít start either. Although it is not good on the EGR valve to idle your Mercedes Benz, you can start your Airstream which gives a little boost to your house batteries to help give your house batteries a little charge in case you run a little low.

I donít believe there is any cutoff or warning on any Airstream from the factory for when the batteries discharge a certain point.

Wish we would have done a few more trials in the driveway just to learn how things work before we headed out on our first couple camping trips. I think we would have had a few less learning curves had we done that.

Good luck on your trip!
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Old 01-17-2021, 02:02 PM   #14
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You don't need to start the engine to start the generator. Just push the battery-connect button on the dashboard.
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Old 01-17-2021, 03:44 PM   #15
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Didnít mean you have to do that to start the generator. Just if your batteries dip a little low to where the generator wonít start, if you start your engine it will charge the house batteries sometimes enough to start the generator. At least thatís how our 2014.5 is.
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Old 01-18-2021, 06:48 AM   #16
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You don't need to start the engine to start the generator. Just push the battery-connect button on the dashboard.
Hi Titus
Are you saying the "Battery Connect" switch on the dash works in reverse?
You can use it both to start the chassis if that battery is low or can use to start the generator if the coach battery is low?
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Old 01-18-2021, 09:22 PM   #17
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Never mind Titus, I forgot about the battery connect button. I thought you werenít understanding that I was not meaning you have to start the RV to start the generator. Reread your comment and now I see what you are saying. Good point.
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Old 01-19-2021, 07:47 AM   #18
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4DXS4,
Here is my understanding:

The battery switch on the dash 'forces' the Battery Isolation Manager to connect the coach and chassis batteries. Under normal conditions the BIM charges one set of batteries (coach or chassis) if it detects high voltage (indication of charging) on one side and low voltage (indication of needing charged) on the other side. Pushing the button connects the two sets of batteries regardless of the state of charge of either set of batteries.

There is the danger of running down the chassis battery when starting the generator, and not being able to start the Sprinter engine. But if the chassis battery was not charged enough to start the generator, it probably wouldn't have started the Sprinter either.
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Old 01-19-2021, 09:38 AM   #19
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Bottom line:

Get new batteries installed. Then, if you drive daily and systems are working as intended, the batteries will be charged when you stop for the night.

The GT's (like yours) are known for being a high battery user, this is likely due to the large fridge. If you can separately turn off your freezer, this will save some power. Keep your inverter off at night if at all possible as it will drain as much or more than the fridge.

Then enjoy your rig.


------------------



PS: If the battery axiety persists after a few trips, the only real solution is coverting to pricy lithium batteries. But in addition to costly batteries, that conversion includes expensive charging components to be changed out and potential cold-weather concerns if the batteries remain outside the heated van. But let's not jump ahead to that now.
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Old 01-19-2021, 08:08 PM   #20
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We have found that the 2 group 24 AGM batteries and 200W solar works for how we use Titus. I put in new AGM's shortly after we got it - 7 years, 70,000 miles, and ~150-200 nights of usage ago. We have stayed at electric sites probably 25 days max, and have used the generator for < 50 hrs. So I'd spent some time with your rig to see what you need before investing in lithium.
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