RV Battery

[Mark_66f816a205900]

I purchased a 2025 Forest River Salem Lite RV and I would like to add an additional battery. I have a solar unit on the roof and thinking for boondocking when not using the generator I should add another battery. Present battery is a Interstate one and adding another running parralel with each other would give me more battery power. Not sure where to get the extra box, but I will google. Open to advice as a RV newbie

 

[bikendan]

Moved thread from the General Community Discussion section to the Electrical, Charging Systems and Solar sub-forum since the OP's questions are specific to that particular sub-forum and are not general community questions.

 

[NoviBill]

Right now LifePo4 batteries are about the same price as AGM ($200/100 amp hours)

*** https://a.co/d/dmMtwYa $160 for 100 amp same as I purchased 6 months ago for $210

Your newer rig should support the LifePo4 directly for charging (plugged in 30amp and Solar).

The advantages for LifePo4
- 2x the useful power - 100 amp hours is 100 usable amp hours (vs AGM where 100 amp hour battery will be damaged each time it goes below 50% charge).
- Longer cycle life (2-5x depending on what you read)
- Less than half the weight - so 2 LifePo4 will weight less than your current battery

Disadvantages:
- You cannot charge them below 32f (yes you can buy heated LifePo4 but 3x the price of cheap ones)
- You need to protect them form temperatures below 10-20f (read battery manual)

 

[Chuck_S]

Interstate makes a zillion batteries. Most marketed as "marine" are starting batteries, nothing more. True deep cycle battery is what you need and you probably want two for more capacity -- they need to be matched for best performance. Even matched batteries work better with a Off-1-Both-2 switch to isolate them as when paralleled the weaker battery will suck power from the stronger all the time. Run this in either Off or Both. Off isolates them from each other. 1 & 2 settings are less useful.

I see the Lithium battery proselytizers have already descended on this topic.

-- Chuck

 

[TitanMike]

Right now LifePo4 batteries are about the same price as AGM ($200/100 amp hours)

*** https://a.co/d/dmMtwYa $160 for 100 amp same as I purchased 6 months ago for $210

Your newer rig should support the LifePo4 directly for charging (plugged in 30amp and Solar).

The advantages for LifePo4
- 2x the useful power - 100 amp hours is 100 usable amp hours (vs AGM where 100 amp hour battery will be damaged each time it goes below 50% charge).
- Longer cycle life (2-5x depending on what you read)
- Less than half the weight - so 2 LifePo4 will weight less than your current battery

Disadvantages:
- You cannot charge them below 32f (yes you can buy heated LifePo4 but 3x the price of cheap ones)
- You need to protect them form temperatures below 10-20f (read battery manual)

An added benefit to lifepo4 batteries is the fact they fo not off-gas while charging and are safe to install in an out of the way interior, heated area. Lots in pass-thru storage and under beds. Freezing while being used is eliminated. Also far more secure inside.

 

[Aussieguy]

plus you get a lot more usable power from Lifepo4
200ah would be similar to buying 4 of those "Marine deep cycles"

solar from factory can probably just keep up with moderate 12v usage
If you going to boondock regularly.... see if you can get 400-800w of solar
how much you need...................... will depend on where you camp

I added 2 x 370w panels 50amp solar controller and 200ah battery capacity
can camp using the 12v fridge and furnace + lights , slides, jacks etc etc

If you want INverter 120v power to make coffee you might need a bit more battery capacity.

I get along quite well without inverter... when I need power I pay for a campground with power.

 

[Bob K4TAX]

I installed a 2nd battery on our trailer. Good quality, true deep cycle battery.

I use a battery switch to select the preferred operation. I start with the switch on BOTH to allow charging the batteries. Then switch to #1 for normal operation of DC equipmnet. When the voltmeter indicates 12.1 volts, I switch to battery #2. The only time I use BOTH is when charging the batteries. The OFF position is for maintenance or to prevent parasitic loads from discharging a battery.

The same thing can be accomplished by using a "battery isolator". I just prefer the old fashion hardwire battery switch. That's just me and I'm stickin' to it.

Bob.

 

[TitanMike]

I installed a 2nd battery on our trailer. Good quality, true deep cycle battery.

I use a battery switch to select the preferred operation. I start with the switch on BOTH to allow charging the batteries. Then switch to #1 for normal operation of DC equipmnet. When the voltmeter indicates 12.1 volts, I switch to battery #2. The only time I use BOTH is when charging the batteries. The OFF position is for maintenance or to prevent parasitic loads from discharging a battery.

The same thing can be accomplished by using a "battery isolator". I just prefer the old fashion hardwire battery switch. That's just me and I'm stickin' to it.

Bob.

This method has been used for decades in boats, setting both while under way then switching to one when stopped.

Works OK for lead acid batteries but highly NOT recommended with LiFePo4 batteries.

When connecting to both for charging the current rush from one to the other can shut down the BMS, potentially on both.

LiFePo4 batteries have very little impedance unlike lead acid batteries.

Using a dual battery switch with LiFePo4 batteries can be done but when switching it would be best to charge one fully then change to the other battery by switching off first then to other battery. When both are charged then "both" could be used for top balance charging.

I'd highly recommend taking note of this when using the lower end batteries that have become plentiful on the market. Also follow the manufacturer's instructions for connecting in parallel if they even provide them.

 

[JimM2109S]

When connecting to both for charging the current rush from one to the other can shut down the BMS, potentially on both.....

Using a dual battery switch with LiFePo4 batteries can be done but when switching it would be best to charge one fully then change to the other battery by switching off first then to other battery. When both are charged then "both" could be used for top balance charging.

If following TitanMike's suggestion, you will need a switch that is "break before make", meaning that one battery is completely disconnected before the second battery is connected. Many, if not most, marine battery switches are purposely designed to be "make before break", meaning that both batteries are momentarily connected when switching from one battery to the other. This is to prevent damage to the charging circuit that could result from not having a battery inline when switching between batteries.

 

[GolfingDave]

I just do not understand the logic behind having a switch to select batteries in a camper. Now you have to monitor something else. Believe I have read on this forum of people waking up in the middle of the night to switch batteries because the first one got low?

Myself, I put extra batteries in to increase my overall AH capacity without having to concern myself with monitoring them.

Maybe I am missing something?

On a boat? Yes, I can see it as something like the "reserve" gas on a motorcycle.

 

[Aussieguy]

switching batteries can put a stain on the batteries and the whole charging

leave them switched TOGETHER so they charge/discharge together
use the switch to isolate a battery for maintenance etc
IF they do not charge/discharge together the culprit will likely be the connections
sort that out... instead of playing battery balancer

lead acid can tolerate some mismatched battery voltage
the electronics in a Lithium battery won't!
joining two batteries together should always be when they are same voltage
otherwise your cabling, lugs and connection will be severely tested. A lot of amps will be moving around even if your battery is within 1/2 a volt difference

Make before break... was developed for spark prevention
good for enclosed lead acid (Hydrogen fumes) battery compartments and bilges that may have trapped gasoline fumes.... don't know if it servers any other real purpose.

 

[Boomerweps]

I see the Lithium battery proselytizers have already descended on this topic.

-- Chuck

Yes, I are one.

IMO, battery switching is a waste of effort & $$. Useful on a boat where you might be stranded at sea, at a CG, not so much.
Even if you are a true believer in them, it gets really complicated once you go to three or four batteries. Battery (bank) isolation is a different animal.

 

[Chuck_S]

The purpose here of the Off-1-Both-2 switch is to isolate the two batteries when they're switched off. The useful positions are Off and Both. Just ignore the 1 and 2 positions unless one or the other has failed.

If left on the Both position when the batteries are neither charging nor powering the trailer the weaker battery will eventually suck the life out of the stronger. Place the switch in the Off position to prevent this.

No need for fancy electronics but ya gotta remember to switch them Off.

-- Chuck

 

[Aussieguy]

Interstate makes a zillion batteries. Most marketed as "marine" are starting batteries, nothing more. True deep cycle battery is what you need and you probably want two for more capacity -- they need to be matched for best performance. Even matched batteries work better with a Off-1-Both-2 switch to isolate them as when paralleled the weaker battery will suck power from the stronger all the time. Run this in either Off or Both. Off isolates them from each other. 1 & 2 settings are less useful.

I see the Lithium battery proselytizers have already descended on this topic.

-- Chuck

lots of good posts about the switching on/off post

OP asked about battery replacement... "Lithium is an option"
none of the "lithium Crowd"... said you have to buy them ...
just how are we to make that happen? Will the OP's screen burst into flames?

I'm happy with my no frills lifepo4 setup ... it works and I will tell anyone that asks
bought everything on the cheap...... using my own money
as a experiment that so far has been great!

-------------------------------------------------------
unless the original green battery is relatively new... don't add a second battery.
study up and do the math

and don't get a switch. if a battery needs isolation for whatever reason............ Undoing the cable works just as good
-----------------------------------------------------
BTW for the. why go lithium ... lead acid works just fine crowd.
lead acid did NOT work fine for me.
the type of camping I wanted to do and for the space, weight and charging speed I needed.

Why does the "lead acid" peoples think lithium crowd should NOT speak up?

The biggest factor was price.... lifepo4 is so affordable now
if someone wanted to just extend their ability to camp for a weekend ... swapping to a single lifepo4 can work..
More power needed?... get bigger and more batteries... there are sizes to suit a lot of different needs.

 

[Bob K4TAX]

This method has been used for decades in boats, setting both while under way then switching to one when stopped.

Works OK for lead acid batteries but highly NOT recommended with LiFePo4 batteries.

When connecting to both for charging the current rush from one to the other can shut down the BMS, potentially on both.

LiFePo4 batteries have very little impedance unlike lead acid batteries.

Using a dual battery switch with LiFePo4 batteries can be done but when switching it would be best to charge one fully then change to the other battery by switching off first then to other battery. When both are charged then "both" could be used for top balance charging.

I'd highly recommend taking note of this when using the lower end batteries that have become plentiful on the market. Also follow the manufacturer's instructions for connecting in parallel if they even provide them.

The OP seemed to be regarding FLA batteries. My response was written accordingly. We have two 100 aH FLA batteriee installed on our trailer. And I do have a battery switch, used as described.

Yes, if one chooses to use LiFePo4 batteries, circumstances and configuration must be differently.

Bob