House Batteries

[MiamiDreamer]

Good day all,
We are total newbies at RVing an need your guidance.
We have a new to us 2015 Excursion and are needing to change the house batteries. We have a residential refrigerator. We expect to use RV campgrounds, COE, City/State/NP campgrounds, etc. At this time we do not think that we will be boondocking, other than the overnight at WalMart, rest areas or CB. I can see that changing in the future although my husband says he is not interested in boondocking at all (I expect him to change his mind when he experiences the peace and quiet, views and zero/low cost of boondocking).
It is time to change our house batteries and we are not sure wether we should go with 2 lithiums or 4 sealed AGMs.
My biggest fear is if we buy the AGMs, and need to overnight (like from 5pm-9am the next day) the batteries will fall below 50% charge and we will damage them. Our battery reader does not provide a % readout so I am not sure how to make sure that the batteries are not falling below the 50% "safe" area.
If we go to Lithium, will we also need to change the inverter? What else will we need to change if we go to lithium?
Thank you in advance for the guidance.

[JohnBoyToo]

when our four L16 size batteries died, agm, etc.. were WAY too new and expensive... so since our use and res fridge did not dictate those huge heavy L16 monsters, we went with 4 trojan t-105's and have been very happy with them the last 5 years...

[Hatchee]

These monitors are very easy to install.

https://www.amazon.com/s?k=Battery+M...ref=nb_sb_noss

[timjet]

When your battery voltage gets to 12 volts with lead acid batteries you are about 50% capacity.

You might consider switching to 6volt GC batteries. They provide a lot of power for the price. Adding 1.5 ounce of pharmacy grade mineral oil to each cell will make them semi-maintenance free.
If cost is not an issue AGM's are a good option and are maintenance free except don't run them below 12 volts either.
Lithium is expensive. Few RV's have them but from what I've read here they are a good option if you can afford them. A battery charger must be sized for them.

A battery monitor will help you determine when you need to recharge. But until you plan on doing much boondocking monitoring your battery voltage should be sufficient.

We have boondocked for up to 7 nights in a row without a battery monitor and just watching voltage. After a few nights you'll know how long you can go between generator starts.


And you are right, some of the best camping has been boondocking.

[Persistent]

First, you will not damage your batteries by drawing them down below 50%. Yes, I know there are many who religiously believe that and are going to call down the wrath of God on me.

You will get twice as many recharge cycles if you only draw down to 50%. So you may get 600 50% cycles and 300 10% cycles. You will probably get 900 75% cycles.

The important thing is to recharge them soon after discharge. Storing them at low levels will cause rapid deterioration or kill them. This is not true of lithium batteries.

The number of amp-hours of storage capacity determines how long you can go before recharging. You also need to know how much 12 volt power you use overnight to know how many amp-hours of battery you need. Power usage is an individual thing.

I guess you will not deplete your fully charged battery bank in one 8 hour night. Most RV's have enough for two or more nights. But, it all depends on you.

Park your RV in your driveway and test it overnight. You probably have a % discharge meter in your RV somewhere. Almost all do. But if not, get a digital voltmeter at your local hardware store and check the voltage at the battery terminals when batteries are not being charged. You may have to wait a couple of hours for the voltage to stabilize after charging. If the refrig or other appliance is running, voltages will be lower until they stop running.

12.4 volts is slightly discharged.
12.1 volts means about 50%
11.6 volts means about 20%

I wish you good luck and happy trails ahead!

[twinboat]

Your not " Damaging " your batteries by running down below 50% occasionally.

If you ran them to 90% discharged, every time, the life would be cut in half compared to using 50%.

This discharge chart is from Lifeline battery.

[bigchick]

you have lots of options. i am assuming you currently have 4 batteries that you are planning on replacing. i don't know what type they are and how hard they are to get to to check and fill water as required.

you've already mentioned lithium. they will probably also require a new converter.

many people recommend 6 volt flooded golf cart batteries. based upon all the recommendations these are certainly an option (if they will fit).

you can also use deep cycle flooded 6 volt or 12 volt in many sizes. again if they will fit

the flooded batteries require periodic maintenance. none would require a converter change.

you can get all the same sizes as the flooded batteries in AGM. they are functionally equivalent but the biggest advantage is they do not vent and do not require the same amount of maintenance. but they cost about twice as much. and they can use the existing converter.

for nearly same price as the flooded batteries you can get maintenance free flooded batteries. these claim to do minimal venting and do not have the option to add water. we have 2 of these (group 27) and we have a residential refrigerator. if you put 4 of these in you would be just fine for the type of camping you do. in 5 years of using these batteries i have not had any acid on them and have never added water. they are sealed so i can't add water. i check once a year for corrosion and have not had any. i am quite impressed with them. they may not be the highest capacity batteries but if you put 4 in you will have lots of capacity. again no change to converter.

[YC1]

Some great advice already so here is my two cents.

Take pictures before touching a cable. Use a voltmeter and take measurements everywhere in the battery compartment and write those down on the printed picture. Insert in a page protector and put where you won't forget it. Or make a copy and hang it in the battery compartment.

Vent the area well before doing anything. Wear safety goggles. Remove the negative terminals first, then the positive cables.

Use any handy tools to clean the cables so they shine like new. Clean and tighten any cables you find nearby on posts.

Follow the negative leads to the frame or areas where they combine onto post etc. Same treatment.

Now that things are even cleaner and tighter than factory new, replace your new batterise.

End of public safety announcement:

[Tha_Rooster]

Originally Posted by Persistent

First, you will not damage your batteries by drawing them down below 50%. Yes, I know there are many who religiously believe that and are going to call down the wrath of God on me.

You will get twice as many recharge cycles if you only draw down to 50%. So you may get 600 50% cycles and 300 10% cycles. You will probably get 900 75% cycles.

The important thing is to recharge them soon after discharge. Storing them at low levels will cause rapid deterioration or kill them. This is not true of lithium batteries.

The number of amp-hours of storage capacity determines how long you can go before recharging. You also need to know how much 12 volt power you use overnight to know how many amp-hours of battery you need. Power usage is an individual thing.

I guess you will not deplete your fully charged battery bank in one 8 hour night. Most RV's have enough for two or more nights. But, it all depends on you.

Park your RV in your driveway and test it overnight. You probably have a % discharge meter in your RV somewhere. Almost all do. But if not, get a digital voltmeter at your local hardware store and check the voltage at the battery terminals when batteries are not being charged. You may have to wait a couple of hours for the voltage to stabilize after charging. If the refrig or other appliance is running, voltages will be lower until they stop running.

12.4 volts is slightly discharged.
12.1 volts means about 50%
11.6 volts means about 20%

I wish you good luck and happy trails ahead!

It’s my understanding op is talking about agm not wet cell. They are 2.43 volts per cell not 2.12 so your discharge figures are a little off.

[Tha_Rooster]

Originally Posted by bigchick

you have lots of options. i am assuming you currently have 4 batteries that you are planning on replacing. i don't know what type they are and how hard they are to get to to check and fill water as required.

you've already mentioned lithium. they will probably also require a new converter.

many people recommend 6 volt flooded golf cart batteries. based upon all the recommendations these are certainly an option (if they will fit).

you can also use deep cycle flooded 6 volt or 12 volt in many sizes. again if they will fit

the flooded batteries require periodic maintenance. none would require a converter change.

you can get all the same sizes as the flooded batteries in AGM. they are functionally equivalent but the biggest advantage is they do not vent and do not require the same amount of maintenance. but they cost about twice as much. and they can use the existing converter.

for nearly same price as the flooded batteries you can get maintenance free flooded batteries. these claim to do minimal venting and do not have the option to add water. we have 2 of these (group 27) and we have a residential refrigerator. if you put 4 of these in you would be just fine for the type of camping you do. in 5 years of using these batteries i have not had any acid on them and have never added water. they are sealed so i can't add water. i check once a year for corrosion and have not had any. i am quite impressed with them. they may not be the highest capacity batteries but if you put 4 in you will have lots of capacity. again no change to converter.

One difference between agm and flooded they have a different charging rate and charging limits. Flooded are 2.12 volts per cell and agm are 2.43 I believe when fully charged.

[Gary RVRoamer]

Good advice from Persistent and twinboat.


I think Rooster's volts/cell are inaccurate. The optimum charging voltage for an AGM is 2.25-2.35 volts/cell while a flooded cell is typically 2.40-2.45 volts/cell. Not very significant in the big picture. If measuring battery state, a 12v AGM is very close to a flooded, rarely more than 0.1v difference in total, so the values Persistent gave are adequate for estimating.

[twinboat]

Originally Posted by Tha_Rooster

One difference between agm and flooded they have a different charging rate and charging limits. Flooded are 2.12 volts per cell and agm are 2.43 I believe when fully charged.

2.43 volts per 6 cells = 14.58 volts. That's not AGMs resting voltage.

[Tha_Rooster]

Originally Posted by Gary RVRoamer

Good advice from Persistent and twinboat.


I think Rooster's volts/cell are inaccurate. The optimum charging voltage for an AGM is 2.25-2.35 volts/cell while a flooded cell is typically 2.40-2.45 volts/cell. Not very significant in the big picture. If measuring battery state, a 12v AGM is very close to a flooded, rarely more than 0.1v difference in total, so the values Persistent gave are adequate for estimating.

I’m sorry but I have 4 agm house batteries and every single one says on top “2.43 per cell”.

[twinboat]

Originally Posted by Tha_Rooster

I’m sorry but I have 4 agm house batteries and every single one says on top “2.43 per cell”.Attachment 282799

That chart is charge and float voltages.

Has nothing to do with resting voltage.