Load Testing Batteries/How low can they go?

[bls72bmw]

Just pulled home a fresh to me 2017 16" Base Camp with the original AGM Interstate batteries.

How can I load test them prior to a trip this Spring so I know if they are doing OK or not?

What is the lowest they should be allowed to get?

[CBWELL]

Take them to an Interstate battery store or dealer and they should be able to test them and give you the results. Some AutoZone stores also do this.

[OTRA15]

Welcome to the forum!

Here is a good resource for general info on RV batteries:

http://www.batteriesnorthwest.com/batteryschool.cfm

It is recommended that the batteries not be allowed to go under 50%, or about 12.2 volts [with the reading done at least 2 hours after the charging current is removed]. [See the first page at the link above]

For that 2017 BC you might as well buy new batteries to start things off right -- the likelihood that the previous owner(s) maintained the batteries well is very low IMO.

Good luck.

[bls72bmw]

Pulling them out! ouch...
That's the professional way to do it....yet I"m not going to pull them out and haul them to the store quite yet.
LOL

Just being honest

They dropped rather quickly to 12.5 today after a very light use. Prolly do need to be swapped...

[wulfraat]

You might consider putting them on a high quality charger for a week with desulphation cycles. I use a BatteryMinder for my 2 lead aside batteries in my diesel truck (keep it on a charger 24/7 when not in use).

Factory batteries will be 4 years old in July and still hold 12.8 volts.

[1StreamDream]

I suggest you get your own tester, they are fairly inexpensive now days and that allows you to monitor and test easily, whenever you want, and any of your vehicles. Mine has certainly been worth it, I got a no-name device off Amazon, there are *many* to choose from in this price point. If it says bad, then I pull the battery out and have Napa, or autozone test and confirm. So far it’s been very accurate and trustworthy (3 bad batteries have been identified correctly).

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[OTRA15]

Good suggestions . . . if labor time is free . . . and you have all the time in the world . . .

4-5 year old batteries . . . with an unknown provenance . . .

Keep it Simple, Stu . . .

New batteries . . . no-brainer . . . reward much greater than cost IMO.

Out.

[Bill M.]

Just buy new batteries. At that age with the history of a trailer that has been sold twice those batteries are toast. And I would not believe a load test that said they are good. You can either do the change yourself or find a store that will do the swap.

[bls72bmw]

Thanks team,
Since I have a while before the season starts...(I'm in Minnesota) I'll hook them up to an OptiMate 7 (super fancy charger) and see what it says.
I plan to plug it into the Solar Port unless that's not right. The OptiMate should be able to handle a slow deep charge when they are hooked up in parallel in the unit.

Thanks for helping a new person everyone.

[uncle_bob]

Hi

Two very different questions:

1) How low a charge level should you let them go to in normal use? Opinions vary, but 50% / 12.0 to 12.2V gets a lot of voltes.

2) How low a capacity should you allow them to get to before you scrap them out? The likely came from the factory with about 105 to 110% of the rated capacity. The battery manufacturers call 80% "done". A lot of RV folks go further. It depends a bit on your use profile.

The only real way to check capacity is to run a discharge test and monitor the results. You can set up to to do this yourself. Indeed, taking them over to a shop may be more practical. Either way you should get a "capacity" number in amp hours. Compare that to the original ~100AH and make a decision.

They may also give you a number in terms of "cold cranking amps". For an RV application, this number is not a lot of use. It's a high discharge number and you pretty much always are in a low discharge mode.

Capacity is not the only number you likely care about. Batteries also have a self discharge rate. Indeed this is related to capacity, but it's not the same thing. A battery that goes flat all on it's own in < 1 month probably isn't what you want in your RV ....

Bob

[rucos]

I vote with no lower than 12v .... my son just bought a nice used Coleman tent trailer and set up in my driveway for a few days. I went out and turned on lights ...had fridge running on propane (electric brain)...filled water tank and used the pump to drain slowly.... and then ran the furnace for several hours.....several times.
Basically I pretend to be "off grid" for 2 days and use my multi meter to keep an eye on battery levels etc. His interstate battery was in good shape. Told him his tires were garbage...LOL.
This also allowed me to discover a pump leak...loose wire on fridge ...small issue with grey tank holders....sanitize fresh water system. The trailer is now ready for an easter camping trip. (he bought new tires yesterday!)
I do this with the airstream too from time to time. Since its at home I unplug it and go off grid for a couple of days..... this is as OTRA15 says a KISS solution...LOL

[JohnTF]

Forums are getting / well the media / schools / etc. has the general public minds buggered up , so why bother answering questions .

Do not want to take out ,
Do not want a pro ,
Do not believe a test ,
Believing general info and applying to all batteries ,
Then spending too much on the wrong gear ,

Go and get educated on whatever you are living off of , then get some test gear , then get the manufacturer's specs. on what you are working with , science & specs. are not a belief issue !
Then you do not have to / should never believing anything --- learn & understand , then you do not have to rely on - believing , rumors etc.

I will check out the link to the battery school .
Another good source is https://batteryuniversity.com/

My last battery bank Trojan L16 lasted 14 yrs. ran air conditioning , everything , living full time , that does not happen without learning & properly setting up a system

[SSquared]

I have Lifeline AGM batteries. One of the good things about Lifelines is they publish a good technical manual. That manual says for their deep-cycle AGM batteries, the typical "load test" is not a good way to judge battery health. Instead, you should do a run-down test at 25 amps, and they tell you how many minutes the batteries should last.

I don't know if Interstate publishes anything equivalent for your batteries, but I would hope so.

The key to the Lifeline run-down test, of course, is being able to measure 25 amps (or 50 if you have two batteries in parallel). My trailer has an aftermarket current shunt that does the job. (That's a very useful thing to have if you are going to be camping off-grid a lot).

[tjwoods1]

I like the idea of having a battery tester like the one you link to at Amazon. I have two 6v Golf Cart batteries wired in series. The battery tester you have a link to is a 12v tester. Would that tester work with the two batteries - or would I need a 6v tester for each battery.

[tjwoods1]

The link I am referring to was posted by 1StreamDream.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[idoco]

The battery testers used at most auto parts stores are generally for testing starter batteries. To accurately test deep cycle battery capacity you need to do a discharge test.

Easy way without moving them.

1. Charge to 100%
2. Take the C20 capacity of your battery and divide by 20 (e.g. 100AH/20H = 5A). This is the load that you should aim to reproduce below.
3. Multiply #2 by 120V to get the wattage for the test. In the example above that's would be 600W (5A x 120V).
4. Find a safe load that is around #3. This could be a small heater, six lamps plugged in with 100W light bulbs, etc.
5. Find a non-digital clock and set it to 12:00
6. Take a look at the automatic cutoff voltage for your inverter. You want it to be around 10.5V.
7. Plug in your load and clock to the trailer inverter circuits. (Make sure the trailer is not on shore power.)

The load will slowly discharge the battery. When the voltage drops below 10.5 the inverter will shut down the battery draw. The battery is now "empty". Read the hours elapsed on the clock.

You now have your C(fill in the hours) rating for your battery. You can compare to the published C10, C20, etc for a new battery and de-rate your actual battery capacity appropriately.


*A charged 12V battery is ~12.7V @100% and ~11.8V @0%. This is the open circuit voltage. The voltage you would see if there is no load on the battery

*1.75V/cell or 10.5V is the voltage of an "empty battery" under load.
*Capacity in amp/hours is a function how fast you discharge the battery. Slower discharges will have larger capacities. Try to mimic the discharge rate that you expect with your use to get the best estimate.

*Yes...you shouldn't regularly discharge lead acid batteries 100%. 50% is recommended for routine use. However, a single deep discharge that shuts off when cells reach 1.75V under load should be fine. If you want a little extra piece of mind you could change the cutoff voltage to 10.6-10.7.

[OTRA15]

Originally Posted by bls72bmw

. . .
. . . I'll hook them up to an OptiMate 7 (super fancy charger) and see what it says.
. . .

Thank you OP please keep us updated.

[1StreamDream]

Originally Posted by tjwoods1

I like the idea of having a battery tester like the one you link to at Amazon. I have two 6v Golf Cart batteries wired in series. The battery tester you have a link to is a 12v tester. Would that tester work with the two batteries - or would I need a 6v tester for each battery.

I looked up the current Amazon listing, it does say the tester will work with both 6v & 12v batteries, and it cites a bunch of industry standard test profiles it uses. I agree with another post that reminded us these inexpensive testers are targeted at automotive (not deep cycle) so some caution is appropriate. The unit has some form of a deep cycle setting for a test (so it says) but I can't offer any other detail. I still think they offer a valuable reference regarding the overall health of the battery, but I would not count on a specific amp hour rating verification, or any kind of formal certification. Need a better test/tester to get that. For what its worth, my use has all been with 12v batteries.

"The latest iBT100 12 Volt Automotive Battery Analyzer from Vident is dedicatedly developed to test 6V & 12V regular flooded, AGM flat plate, AGM spiral and gel batteries. And covers most of the battery rating standards: CCA, BCI, CA, MCA, JIS, DIN, IEC, EN, SAE standards, for accurate battery health status checking."

[bls72bmw]

These look reasonable and not crazy expensive.
Any feedback? (though the posts are a bit offset from the OEM batteries_)

https://www.oreillyauto.com/detail/c...j/34magm?pos=0



Going to do a 'test use' of the batteries as one of the above gents suggested...use the trailer in the backyard for a weekend and see how the batteries do in real-ish world conditions. Also as a way to get used to the camper.

I think it's a lot of overthinking we all do on this stuff...I'm in the middle of a city and will do a demo, if they work, great, if not, get new ones. LOL.
Too much brain space can be dedicated to the Rabbit Hole where-as I have a million other things to get on with.
Of course, to each their own, that's what having a nice discussion here does! Thanks for the input.

[OTRA15]

Originally Posted by bls72bmw

. . .
Thanks for the input.

Thank you OP for the update late last night.

Happy Trails.