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dc92974

How long should batteries last

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This question is asked all over the internet but there are so many variables that I'm having still having trouble understanding if I have a problem.

Background...
I recently moved off grid, I've always been plugged into shore power up to this point. My stock rv batteries would barely hold a charge for 24 hours. I could run the generator to charge them up in the evening until the battery status was 4 full lights. The next day after work they would be down to 1 light. They are the stock batteries and were ~5 years old so I figured they were due to be replaced anyway.

I replaced them 2 Vmax 6V 225ah batteries (https://www.vmaxtanks.com/V6-225-6Volts-225AH-Deep-Cycle-High-performance-AGM-Battery-_p_48.html). I also added small solar system with 2 100w solar panels. With the solar charge controller I gained the ability to see the actual voltage rather than just the 4 light system my camper has (guessing it isn't very accurate).

 

Today...
With the new batteries and solar setup I can charge the batteries in the evening until they say 100% (~13.1v). In the morning they will have already dropped to about 70% (12.7v). By the time I get home from work they will have dropped to about 60% (12.6v) depending on how much sun there is. (I only get 2-3 hours of sun this time of year) The battery status lights on the camper will show 3-4 stars through the whole day.

So even with all the new stuff my batteries only last about 24 hours before they need recharged? I have almost everything turned off. The thermostat for the heater and fridge use electricity, the solar charger uses some when the sun isn't shining but that's about it. The water pump is on but it probably only runs 5-10 seconds total per day. I have the breakers turned off for everything but the inverter and I haven't even been using the led lights trying to save electricity.

 

I'm not sure what to think, seems like batteries should last longer than 1 day. I'm also not sure what to think that by looking at the voltage I'm dangerously low after 24 hours but looking at the lights on the control panel I still have 3 lights? Any thoughts would be appreciated. It doesn't seem right to have to run the generator for hours every night to a few small electrical devices.

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Is your fridge set to gas or electric?  If you are running the fridge on electric through your inverter,  that is a 300 watt draw when the fridge runs.  Also, your inverter will have a static draw, depending on the size of inverter it could be up to 50-75 watts.   You could probably consider upping your solar capacity.....if possible.  Do you have the ability to measure how much your rig is drawing?  I would guess with the info you provided, you are just using more amps than you are replacing.

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I'm not sure where you're getting your voltage figures from.

Ordinary lead acid battery individual cells provide 2.1 volts each when fully charged, so a battery of six of them will show 12.6 or 12.7 volts (depending on meter accuracy) at full charge IF it's been at rest for a couple of hours, with no current going in or out during that time. 

13.1 volts is a float charging voltage.  If you're seeing 13.1 volts, it doesn't necessarily mean your battery is fully charged,  it means a charging source, whether solar or shore power or your generator is providing power to the system.

With 225 amp hours of batteries, you should have 110-115 amp hours (50% cycle) to use before you need to recharge it again.

To really know what's going on, you'll need to measure actual amp draw of everything you run and figure amp hours based on how long it's run.

You say you have to run your generator for hours?  Are you using one of those old, simple converters to recharge your batteries with the generator?  A high capacity modern smart charger, with bulk, absorption, and float voltages will pay for itself fairly quickly in gas savings.  Something like a 40 or 60 amp charger.

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The fridge is set to gas. I could flip the breaker for the inverter when the generator isn't running to see if that makes a difference. I would like to upgrade my solar system probably next summer, for now I'm trying to learn as much as possible so I can make good decisions on purchases.

With "what I know of" that's drawing power they should last a lot longer right? Maybe my focus now needs to be to figure out how to monitor how much power (watts?) I'm drawing from the batteries. Maybe there's something I don't know about that's drawing off the batteries.

Is if fair to say I should pretty much ignore the led battery lights on my camper's control panel? They probably are not very accurate compared to using the voltage?

 

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19 minutes ago, dc92974 said:

Is if fair to say I should pretty much ignore the led battery lights on my camper's control panel? They probably are not very accurate compared to using the voltage?

Those battery lights commonly found in nearly all RVs are of almost no value at all. As a retired tech I would rate them anywhere from inaccurate to totally useless. 

Are you using the furnace at all? If you are the blower is probably the thing drawing down the batteries. The water pump doesn't run long enough to make much load unless you take a long shower. The water heater and refrigerator both use 12V power to operate the controls but it is a very small load and should take days if not weeks to deplete your batteries. Keep in mind that 200 watts from your solar is only possible with clear sky and the panels at 90° to the sun. For 3 hours per day of sun that isn't much even if they are in full sun. It would also be helpful to know more about the inverter. What make and model do you have?

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Watching the lights does not tell you anything about battery SOC. (State of charge).

i would highly recommend installing a battery monitor such as the one from Bogart or I ve heard people recommend the link meter. This will measure total amps "in" and total amps "out". 

I to would suggest turning the inverter off until needed, it has a idle current draw.

is your solar charge controller programmable, if so what volatage are the batteries being charged. Each battery manufacture has different requirement for charge voltage. 

Sounds to me that it might be possible that the batteries are not getting 100% charged. In addition the inverter draw when not in use does not help. 

Hope this helps, I am no expert but have researched on line .

Jim

 

 

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I got the voltages from the battery mfg website, they seem to agree with what the Renogy charge controller thinks too. (https://www.vmaxtanks.com/assets/images/technical info folder/state_of_charge_chart.pdf)

I've replaced the charge controller that came with the trailer. I have the Progressive Dynamics PD9245CV now. (https://www.amazon.com/Progressive-Dynamics-PD9245CV-Inteli-Power-Converter/dp/B000GANZZ6). It's a 45 amp charger and has different modes depending on the battery state.

I tried to get my batteries to 100% over the weekend, here's a break down.

10/20 15:30 12.8v (my starting point about 78% capacity)
10/20 15:30-19:30 Charging at 14.3v
10/20 19:30-20:30 Charging at 13.6v (Docs say it does this to charge the battery from 90-100%)
10/20 20:30 Turned off generator for night
10/21 09:00 Batteries at 12.74v. Turned generator on again.
10/21 09:00-11:00 Generator running charging at 14.3v
10/21 11:00-17:30 Solar panels charging 13-14.5v
10/21 17:30-18:00 Generator charging at 14.3v
10/21 18:00-20:30 Generator dropped to 13.6v
10/21 21:00 Everything off for the night. Batteries at 13.05
10/22 06:00 Wake up batteries at 12.74v again

Now I'm at work, it's sunny today so when I get home tonight the batteries will probably be in the 12.7-12.8 range. Ready to run the generator for hours again 😞

 

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15 minutes ago, Kirk Wood said:

Are you using the furnace at all? If you are the blower is probably the thing drawing down the batteries. The water pump doesn't run long enough to make much load unless you take a long shower. The water heater and refrigerator both use 12V power to operate the controls but it is a very small load and should take days if not weeks to deplete your batteries. Keep in mind that 200 watts from your solar is only possible with clear sky and the panels at 90° to the sun. For 3 hours per day of sun that isn't much even if they are in full sun. It would also be helpful to know more about the inverter. What make and model do you have?

The furnace is on but the temp is set to 40 and its not that cold yet so it doesn't turn on. The water heater gas and electric are turned off. No hot water... so no showers either :-). I just added my inverter info and some charge rate detail over the weekend as you were typing.

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Your wake up voltage is good. Battery was pretty much at rest and showing 12.7 v  could not ask for much better than that. 

If you run the generator the same time your solar is providing power whichever one has the higher voltage will be the one providing amperage. So both with the sun shine is wasting fuel. 

I still would suggest buying Trimetic TM 2030 battery monitor. Using it is the only way to know for sure the condition of your batteries. Has lots more information available too. 

Jim

 

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If you really want to know what's up with your batteries State Of Charge, forget both the 'lights' and the voltmeter and get yourself a good battery hydrometer, one with a built in thermometer so you can adjust for temperature.

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1 hour ago, Optimistic Paranoid said:

I'm not sure where you're getting your voltage figures from.

Ordinary lead acid battery individual cells provide 2.1 volts each when fully charged, so a battery of six of them will show 12.6 or 12.7 volts (depending on meter accuracy) at full charge IF it's been at rest for a couple of hours, with no current going in or out during that time. 

13.1 volts is a float charging voltage.  If you're seeing 13.1 volts, it doesn't necessarily mean your battery is fully charged,  it means a charging source, whether solar or shore power or your generator is providing power to the system.

 

3 minutes ago, Optimistic Paranoid said:

If you really want to know what's up with your batteries State Of Charge, forget both the 'lights' and the voltmeter and get yourself a good battery hydrometer, one with a built in thermometer so you can adjust for temperature.

Optimistic Paranoid, I'm confused (which is why I'm here), maybe I have a different type of battery than you're talking about? The voltage figures come from the battery mfg and the battery is also completely sealed. I don't think there's any way to use a hydrometer on it because I can't get to the fluid?

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Where are you getting your state of charge from? You really need a battery monitor such as the trimetric. 

Edited by Ronbo

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Another option for battery monitoring....easy to install and use even has Bluetooth capability to setup and monitor from your smart phone.

https://www.victronenergy.com/battery-monitors/bmv-712-smart

YouTube intro video....https://www.youtube.com/watch?v=2vA-EjSSBVA&list=PLnKCJA0l3E6bCC56dVlVIQO1s3VxwZmbp&index=6

 

Here is a link to the aforementioned Bogart TriMetric battery monitor....

http://www.bogartengineering.com/products/trimetrics.html

 

Edited by DesertMiner

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42 minutes ago, dc92974 said:

 

Optimistic Paranoid, I'm confused (which is why I'm here), maybe I have a different type of battery than you're talking about? The voltage figures come from the battery mfg and the battery is also completely sealed. I don't think there's any way to use a hydrometer on it because I can't get to the fluid?

You're right.  I saw the part about them being 6 volt deep cycles, and didn't notice they were AGM.  In the immortal words of Gilda Radner as Roseanne Roseannadanna, "Never Mind!"

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1 hour ago, DesertMiner said:

Another option for battery monitoring....easy to install and use even has Bluetooth capability to setup and monitor from your smart phone.

https://www.victronenergy.com/battery-monitors/bmv-712-smart

Hmm, that's pretty intriguing. I like the idea of bluetooth. That would let me use it and get comfortable with it before a permanent install. Right now everything is setup under my skirted trailer. Same idea, learning what I need/want and then in the summer I'll do a full install when the weather's nice.

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I'm a little curious about the state-of-charge table for the Vmax batteries. Even though they are AGM batteries I believe that they are still lead-acid technology, so they should track pretty closely with flooded cell numbers. I really wonder if your 12.74 volts in the morning represent a 70% SOC or something much better. With my flooded cell batteries I would consider that to be essentially fully charged. I've seen several other state-of-charge tables for various AGM batteries, and I can't find any that list voltages as high as the Vmax charts. Unless they'd got some sort of modified chemistry I would take them with a grain of salt. 

As others have noted, a battery monitoring system is necessary to really determine state of charge and loads during the day.  With the inverter off and only running the fridge on gas, the water pump occasionally, and a few lights, you should  be doing quite well with your solar system, and definitely not have to run a generator 3-5 hours each day.  

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14 minutes ago, mptjelgin said:

I'm a little curious about the state-of-charge table for the Vmax batteries. Even though they are AGM batteries I believe that they are still lead-acid technology, so they should track pretty closely with flooded cell numbers.

I looked up some other charts and I see what you mean. The only thing I can come up with is the inclusion of temperature? Most of the charts I saw seemed to be for a set temperature like 80F.

We do have pretty big temp swings right now. 50-60 for the high in the afternoon and 25-35 for the low in the morning. It's a little less of a change under the skirting but it's still probably a 20 degree temp difference when I check before I go to bed and get up in the morning. Could the temperature be what I'm seeing in the voltage differences?

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For serious off grid camping. Do continue your off grid electric arsenal to add a battery monitoring system. The Bogart unit recommended, had been a well used and understood highly regarded unit. Victron is not a new kid to the block, and also have a good rep. One has more goodies then the other to play with, and only you can decide which one you'd want to run with. 

And remember that the voltage being reflected is 'non resting' voltage. Suspect the battery Voltage to SOC chart you're looking at is referring to 'at rest' voltages. Which because of the way we boon dock, is not very easy to obtain:)! 

Once you get you choice of energy monitoring in place. You can then go thru various systems and disconnect them, to see where you are consuming Amp Hours in a non value added way. Trim this down as much as possible. And then go thru some energy auditing days of camping, especially overnight, and learn your actually energy consumption. This will allow you the ability to decide how to mange your battery to balance usage vs charging:)!

Best o luck to you,

Smitty

 

 

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Thanks for all the replies and help. This is slowly morphing into a battery monitor post so I can get some more detailed info so... I have hopefully a basic question.

With these battery monitors they all seem to also have their own brand of solar charge controller as well. I have a renogy one which isn't going to plug and play with any of them, will I lose functionality I need with a battery monitor because of this? Do I need to purchase a charge controller from the same vendor, that would be kind of sad since the Renogy one isn't even broke in yet.

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Some battery monitors are integrated with solar controllers (or inverter remotes) but there are plenty of stand-alone monitors. The  Bogart Trimetric 2030 is a stand-alone unit and will not interfere with your solar controller. 

 

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You can mix and match components from different manufacturers. The TriMetric, the Victron BMV, or another battery monitor of your choice will all get the job done. It’s more important to have a “shunt” type battery monitor to give you correct info as to what is going into your battery as far as “charge” and what you have  used or “discharged”  from your battery over a period of time.  Staying with one “brand” will sometimes make communication between different components easier and more user friendly and in some cases you get some added functionality. 

Edited by DesertMiner

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I ordered the Victron BMV. Should be here this weekend and I can install it ans see if the new data source sheds some light on what's going on.

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7 minutes ago, dc92974 said:

I ordered the Victron BMV.

You'll like this! I mounted mine to a nice piece of wood that I finished using a small L bracket, looks very cool next to the bookend on the shelf. Very accurate, useful, & informative read outs. Items like this should be common among RVers.

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I’d not even mount the Victron meter, wish I hadn’t. I VERY seldom look at the meter, with the bluetooth you don’t need the meter. It’s also easy to take it with you to your next rig.

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