25SRK 2025 trying to understand battery life

[sdp1234]

Testing out our new camper and how long the batteries will last.
I get completely different numbers when I look at the multiple monitoring systems within the camper. Currently, I only have one solar panel on top (two 200ma and we have 2 100 mA lead acid batteries that came stock with the unit.


One app shows 11.9 v
One app shows 12.1
The on board display shows 12.1
The control panel shows that the battery is good

If it is really 11.9 the. It's below 50% from what I understand. If so that shouldn't be listed at good?


Should I abandon my test at this point in order not to degrade my batteries?

 

[Aussieguy]

get an extension cord and a adapter and plug into a 15-20amp outlet at your house
get the converter going to charge up the battery.


then you can work on working out what all the stuff is

 

[sdp1234]

I plugged it in. I'll resume testing after it is completely charged again

Thanks

 

[Bob K4TAX]

First of all regarding understanding is terminology. The reference to solar panel power is in watts and not ma or milliamps. Battery capacity is rated in amp hours or Ah. With lead acid batteries, you are able to use ~50% of the capacity without risk of damage. For a 100 Ah rated battery one has about 50 Ah of useable capacity.

Now what is an Ah? It is the unit used to measure a battery's energy capacity, indicating how much current it can provide for a specific period of time. For a 100 Ah lead acid battery, FLA - Flooded Lead Acid, using 50% of its capacity, this would be 10 amps for 5 hours. Or 2 amps for 25 hours.

The voltage display, it shows the voltage applied to the battery or the voltage as measured across the battery terminals. The attached chart is an indicatior of battery charge based on measured voltage for FLA batteries. At 11.9 volts this is about ~40% charge state which is below the recommended 50% minimum. ***Battery needs charging. At 12.1 volts this is ~50% charge state which is the lower limit of safe usage. ***Battery needs charging.

With the RV connected to shore power and using the converter to charge the batteries, the charging voltage should be 13.6 volts. After charging, the system should "float" the batteries at 13.1 volts. With the converter off or disconnected, after about 1 hr of non-usage to allow surface charge to dissipate, the battery should measure 12.6 volts.

Define "good"? In general terms, the battery will deliver some amount current and the battery can or should be charged. Nothing you have will actually indicate if the battery can be charged to 100% of rated capacity. Although the display may show "good". What ever that means.

As one stated earlier, plug in the RV to 120 volt shore power and let the converter charge the batteries. It may take 12 to 20 hours to do so, depending on the capacity/charge rate of the converter and condition of the batteries. YOU HAVE CHECKED THE ELECTROLYTE LEVEL (commonly referred to as water level) in the batteries. And then, if a battery has been depleated to below 12.0 volts multiple times, it may never charge to 100%.

As to the "apps", I'm not confident in their information not knowing what and where they measure the voltage. I would more likely trust the on-board display of 12.1 volts. A separate hand held DVM (digital volt meter) with the leads connected direct to the battery terminals is the more accurate way to measure battery voltage.

As to a battery being "good" or "bad", the more reliable way is to perform a load test. Most auto parts stores will do this free of charge. But you have to remove the batteries and take them to the facility for testing.

Bob

 

[sdp1234]

Bob


Thanks for the detailed explanations.



I apologize for the initial post that was submitted in haste. I really should have considered the time that folks put into reading and responding


Crazy thing is that I have a bit of past training in the current, power and resistance. If I sit down with my computer, pencil and paper it all works out. When having a conversation or typing questions my terminology gets all jumbled and it sounds as if I have no clue Doesn't make it from my brain to my fingers or mouth.


I was hoping (2) 100 mAh batteries with one 200w solar panel would last me a weekend or long weekend without shore power. Love the new camper but I don't think I'm a fan of the 12 frig over the Gas\Electric in our previous unit.


Maybe I should simply go with 200-400 mAh of LiFePO4



Typically we camp with power only (no water or sewer)
Weekend or long weekends without needing power will give us more options for last minute camping in our area.

 

[GolfingDave]

Finally, a chart that shows discharging below 50% doesn't automatically kill your battery. Something that is insinuated a lot.

How much shorter? It depends but you will most likely notice it coming on and not just drop dead.

Thanks for the post.



Signed: A dead battery survivor.

 

[Aussieguy]

I was hoping (2) 100 mAh batteries with one 200w solar panel would last me a weekend or long weekend without shore power. Love the new camper but I don't think I'm a fan of the 12 frig over the Gas\Electric in our previous unit.

I have a 200ah battery lifepo4 (Lithium) much better than lead acid

mine will last a weekend of 12v usage including the dreaded 12v fridge
when I installed my battery ... tested the fridge running time... it will last about 60 hours

with your solar 200w will allow you to stay out a weekend ... don't camp in the shade though

Solar will also charge as you drive to next location... so do NOT switch off the solar controller unless you are doing some maintenance


If you need to use the FURNACE and FRIDGE ... you will need more solar

If you want easy camping on 12v (no inverter)

GOOD..
400-600w solar
2 x 100ah Lifepo4

BETTER
800w solar + 50amp MPPT
2x 100ah Lifepo4 batteries

I have the second setup and it I have not had to use generator or shorepower to charge the batteries

------------------------
your solar controller ... is the biggest factor for how many panels
if you got a 30amp controller 400w is about the most solar you can efficiently use

changing out the controller to a bigger one can be easily done

Keep the original controller and use it for a second set of panels
(maybe install a second set in the future)

 

[TacomaJoe]

In totally general numbers, here's my two cents. Your refrigerator will use maybe 80Ah of your capacity a day, solar will replace maybe 50Ah giving you a net loss of 30Ah a day from your total of 100Ah battery capacity. You would get three days with no other factors in the loop.

You're on the right track to work these numbers out for YOUR rig.

I wired in a current shunt on my trailer and highly promote their use. A voltage reading isn't going to tell you if there is a load pulling the battery down or if the solar is charging it.

I don't trust the monitor panel lights. What I did was take readings and compare them to the lights to come up a better idea of what was going on. Works for the battery and by adding 5 gallons at a time into my tanks I could interpret the tank level lights on my rig.

 

[Bob K4TAX]

Bob
Thanks for the detailed explanations.

I apologize for the initial post that was submitted in haste. I really should have considered the time that folks put into reading and responding

Crazy thing is that I have a bit of past training in the current, power and resistance. If I sit down with my computer, pencil and paper it all works out. When having a conversation or typing questions my terminology gets all jumbled and it sounds as if I have no clue Doesn't make it from my brain to my fingers or mouth.

I was hoping (2) 100 mAh batteries with one 200w solar panel would last me a weekend or long weekend without shore power. Love the new camper but I don't think I'm a fan of the 12 frig over the Gas\Electric in our previous unit.

Maybe I should simply go with 200-400 mAh of LiFePO4

Typically we camp with power only (no water or sewer)
Weekend or long weekends without needing power will give us more options for last minute camping in our area.

Lets hope those 2 batteries are 100 Ah each and NOT 100 mAh capacity. (typo?)

From others, 200 watts of solar is at or below minimum needs. While 200 watts may seem adequate, 400 to 600 watts is more realistic. Sun angle, cloud cover and daylight hours will always reduce the "stated rating" of solar panels.

With FLA batteries, 2 of the 100 Ah batteries gives you only 100 Ah of useable capacity. Changing to LiFePO4 @ 200 Ah each, with suitable charging capacity and ability, will give you about 380 Ah of useable battery capacity.

Agreed, I prefer the refrigerator to be AC/LP. Also, all lights should be LED type and not incandecent.

Bob

 

[NJKris]

Bob


Thanks for the detailed explanations.



I apologize for the initial post that was submitted in haste. I really should have considered the time that folks put into reading and responding


Crazy thing is that I have a bit of past training in the current, power and resistance. If I sit down with my computer, pencil and paper it all works out. When having a conversation or typing questions my terminology gets all jumbled and it sounds as if I have no clue Doesn't make it from my brain to my fingers or mouth.


I was hoping (2) 100 mAh batteries with one 200w solar panel would last me a weekend or long weekend without shore power. Love the new camper but I don't think I'm a fan of the 12 frig over the Gas\Electric in our previous unit.


Maybe I should simply go with 200-400 mAh of LiFePO4



Typically we camp with power only (no water or sewer)
Weekend or long weekends without needing power will give us more options for last minute camping in our area.

Here's the problem, you are running milliamp hours! The rest of us have amp hours. I don't recommend model airplane batteries.

 

[Twinboat]

Your told that going below 50% state of charge damages your battery and then they back that up with a chart that doesn't show that.

Is the whole battery industry lying to us about their capacity ?
100% only equals 50% ?
It's all a myth and since Lithium came on the market backed up by them to offset the high price.

You will get twice the life cycles out of a battery only discharging to 50% then if discharging to 10%.
You will get 3 times the life cycles only discharging down to 75%, maybe we should do that.

The point is, an occasional deeper discharge, as long as your not drawing them down lower then 10.6 volts ( 0% ) will do no harm and take 1 day out of your batteries life.

 

[TitanMike]

Your told that going below 50% state of charge damages your battery and then they back that up with a chart that doesn't show that.

Is the whole battery industry lying to us about their capacity ?
100% only equals 50% ?
It's all a myth and since Lithium came on the market backed up by them to offset the high price.

You will get twice the life cycles out of a battery only discharging to 50% then if discharging to 10%.
You will get 3 times the life cycles only discharging down to 75%, maybe we should do that.

The point is, an occasional deeper discharge, as long as your not drawing them down lower then 10.6 volts ( 0% ) will do no harm and take 1 day out of your batteries life.

And to add, if you recharge to 100% as quickly as possible after such a deep discharge damage to the battery will be mitigated somewhat.

If using Flooded Lead Acid (FLA) batteries and finding they are being regularly discharged below the 50% mark it would be a good idea to increase the capacity by adding another battery. If not now, at least when replacement time comes around.

BTW: trying to determine the correct voltage by using multiple measuring devices can be just like trying to determine what time it is by consulting several different watches. As recommended earlier, find a GOOD voltmeter (multi-meter) and read voltages at the battery terminals.

 

[Bob K4TAX]

Your told that going below 50% state of charge damages your battery and then they back that up with a chart that doesn't show that.

Is the whole battery industry lying to us about their capacity ?
100% only equals 50% ?
It's all a myth and since Lithium came on the market backed up by them to offset the high price.

You will get twice the life cycles out of a battery only discharging to 50% then if discharging to 10%.
You will get 3 times the life cycles only discharging down to 75%, maybe we should do that.

The point is, an occasional deeper discharge, as long as your not drawing them down lower then 10.6 volts ( 0% ) will do no harm and take 1 day out of your batteries life.

My old math says 40% is less or lower than 50%. Read what the chart says about operation at 40% and lower.

A fully charged FLA battery is 12.6 volts at 100% charge with no load. At 50% charge the voltage drops to 12.1 volts. So a 100 Ah rated battery, discharged 50%, leaves 50% charge. Thus a 100 Ah battery can only repeatedly supply 50 Ah of current that is equal to 50% of total capacity.

The chart I supplied is not for Lithium battery chemistry, but is for FLA batteries which is what is typically and most often is supplied from the Dealer. I believe the chart is from the Interstate battery site.

If one chooses AGM or Lithium battery chemistry, there is a different set of rules to be followed.

Bob

 

[NJKris]

And to add, if you recharge to 100% as quickly as possible after such a deep discharge damage to the battery will be mitigated somewhat.

If using Flooded Lead Acid (FLA) batteries and finding they are being regularly discharged below the 50% mark it would be a good idea to increase the capacity by adding another battery. If not now, at least when replacement time comes around.

BTW: trying to determine the correct voltage by using multiple measuring devices can be just like trying to determine what time it is by consulting several different watches. As recommended earlier, find a GOOD voltmeter (multi-meter) and read voltages at the battery terminals.

TitanMike is right! While 50% is a good compromise, true deep cycle batteries like golf cart batteries are made to go down to 20% SOC. Full recharge soon after is best practice to ensure longevity. I have 6 years on my FLA golf cart batts (Deka), 30 nights per year use of RV. Hoping I get another year or two on them.

 

[5picker]

Yep, those of us who have camped for many, many years, long before fancy charge monitoring devices, solar and controllers know we occasionally ran the battery(ies) well below 50% SOC and still had a battery(ies) that lasted for years.

We didn't bring them inside and tuck them in every night over the winter. We just used them and we did so without losing any sleep whether we'd get a few more cycles out of them than if we only took them to 50% EVERY time!

 

[tomkatb]

Batteries are not all equil.

There are two types of lead acid. Deep cycle and car batteries. The golf cart 6 volt batteries last longer and are more abuse friendly. Plus often cheaper. Batteries labeled as deep cycle that are not gc batteries are constructed differently. Like car batteries. As an engineer I cannot understand why car batteries are used in rv’s expect they are cheap and available at Walmart. Better for starting car engines.

Solar in the Midwest is kind of iffy. The average 100 watt panel on a great day, not most, on your roof, can produce 25 ah of charge to your system. Clouds, rain and treed campsites are the enemy. Thus your 200 watt system on its best day can provide only 50 ah to the batteries. Your use with a compressor fridge is likely well over 100 ah per day. Likely over 150 ah per day with the furnace. Inverters are power hogs. A 2000 watt inverter could wipe your batteries out in hours.

Without a fancy ampere displaying battery monitor your might not be able to see what is going on.

Watch whatever meter you have in the rv. Note its voltage an hour after the shore power is off! Max should be 12.6. Regardless of what the meter says. I only trust my handheld meter measured at the battery. We have a fancy $30 Bluetooth voltmeter that has historical graphs. I trust that also. Our new batteries have an amp meter built in.

When reading the voltage the solar also should be off an hour!

Since we live in the Midwest we have no solar. However we have a gas/electric fridge and 412 ah (about $1200, premium batteries)of battery storage. We have to use our 2200 watt generator every 3-4 days. In an emergency it will power one air conditioner as well as charge the batteries. And a 400 watt inverter which we never use.

 

[NJKris]

Batteries are not all equil.

There are two types of lead acid. Deep cycle and car batteries. The golf cart 6 volt batteries last longer and are more abuse friendly. Plus often cheaper. Batteries labeled as deep cycle that are not gc batteries are constructed differently. Like car batteries. As an engineer I cannot understand why car batteries are used in rv’s expect they are cheap and available at Walmart. Better for starting car engines.

Solar in the Midwest is kind of iffy. The average 100 watt panel on a great day, not most, on your roof, can produce 25 ah of charge to your system. Clouds, rain and treed campsites are the enemy. Thus your 200 watt system on its best day can provide only 50 ah to the batteries. Your use with a compressor fridge is likely well over 100 ah per day. Likely over 150 ah per day with the furnace. Inverters are power hogs. A 2000 watt inverter could wipe your batteries out in hours.

Without a fancy ampere displaying battery monitor your might not be able to see what is going on.

Watch whatever meter you have in the rv. Note its voltage an hour after the shore power is off! Max should be 12.6. Regardless of what the meter says. I only trust my handheld meter measured at the battery. We have a fancy $30 Bluetooth voltmeter that has historical graphs. I trust that also. Our new batteries have an amp meter built in.

When reading the voltage the solar also should be off an hour!

Since we live in the Midwest we have no solar. However we have a gas/electric fridge and 412 ah (about $1200, premium batteries)of battery storage. We have to use our 2200 watt generator every 3-4 days. In an emergency it will power one air conditioner as well as charge the batteries. And a 400 watt inverter which we never use.

I read on Batteryuniversity.com a while back that a starting/car battery should not go below 60% SOC, compared to deep cycle 20-50% SOC. This may be part of explanation of why people always need to replace car battery. Since I started RVing and learned all this info, I take better care of my car batteries, top them up if they've been sitting undriven for a couple weeks. My F150 gets far less use after towing/camping season.

 

[jlh1958]

Should work if batteries are ok

Bob


Thanks for the detailed explanations.



I apologize for the initial post that was submitted in haste. I really should have considered the time that folks put into reading and responding


Crazy thing is that I have a bit of past training in the current, power and resistance. If I sit down with my computer, pencil and paper it all works out. When having a conversation or typing questions my terminology gets all jumbled and it sounds as if I have no clue Doesn't make it from my brain to my fingers or mouth.


I was hoping (2) 100 mAh batteries with one 200w solar panel would last me a weekend or long weekend without shore power. Love the new camper but I don't think I'm a fan of the 12 frig over the Gas\Electric in our previous unit.


Maybe I should simply go with 200-400 mAh of LiFePO4



Typically we camp with power only (no water or sewer)
Weekend or long weekends without needing power will give us more options for last minute camping in our area.

I have boondocked for years with 2 100ah lead acid batteries connected in parallel with a 100W solar panel. The cheap charge controller managed to keep my batteries charged up just fine. I recently upgraded to a Renogy 200W suitcase solar panel with a 20A charge controller and it works even better.

Just remember the limiting part is the lead acid battery. I am upgrading to 2 100ah LiFePO4 batteries and 2 200W solar panels with a 30A MPPT charge controller to double my capacity and still be able to charge back up to 100% with a few hours of good sun while boondocking. If you want to be independent of campsites with electric, that might be something to consider.

Otherwise, make sure your converter is working properly, check electrolyte (water) levels in your lead acid batteries and plug into shore power. Expect only 2-3 years from lead acid batteries. Less if you drain them below 50%.

Hope this helps!

Happy trails!