Battery Voltage Under Load, is it time to replace?

[bigfatguy]

First off, I realize battery voltage is a very poor indicator of battery health or how much juice is left "in the tank", but until I scrounge up a few hundred bucks for a battery monitoring system, this is the best I have.

My house batteries read 12.6v without any lights on in the RV.

Turn on a few lights (overhead, galley, bathroom) and the voltage drops as low as 12.2.

Turn the lights off, and the voltage recovers to 12.6.

Is this normal? Am I looking at replacing my house batteries?

The main reason I ask is my wife noticed the voltage as low as 11.8 while getting things set up for a trip this weekend... but I think she had every light in the rig on at the same time.

The RV is a 2017 Winnie ERA 170M. The lights are all LEDs.

 

[Ernie n Tara]

Before replacing I'd check the connections and measure directly at the battery. If the same thing is happening at the battery, it's likely bad.

Ernie

 

[Rene T]

Are you checking the voltage while plugged into shore power?

 

[QZ]

Assuming you have a group battery have you checked the specific gravity?

 

[Alpena Jeff]

Hey big fat guy. Welcome to the forum.
Love the name!

 

[Gary RV_Wizard]

The observed voltage will indeed drop substantially as amp load goes up. A relatively small battery shows greater voltage drop than a larger one because a given amount of amps is a greater proportion of its total capacity. Your rig probably has a Group 24 size battery, about 80 Amp-hours total when it was new. It is undoubtedly a marine/RV type battery and they don't have a long useful life in typical RV usage, maybe 2-3 years if you routinely camp without electric hook-up.


If the battery is a year plus old, and maybe deeply discharged a few times in its young life, its capacity has probably dropped somewhat since new.  How much is impossible to guess, perhaps anywhere from 10% to 40%.  Is your on its last legs?  Try the specific gravity test if its is a flooded cell battery (not sealed).  Battery hydrometer sare inexpensive and available at auto parts store and many Walmarts.  But since your battery bounces back to 12.6v, the SG is probably ok.

 

[Kevin Means]

If your indicator is accurate, and your battery's voltage is going from 12.6 to 12.2 volts when only "a few" LED lights are turned on, there's almost certainly something wrong with the battery. When under a load, it's normal for a Lead/Acid battery to indicate less voltage than its true voltage, but "a few" LEDs do not draw enough current to cause such a large drop in voltage from a fully charged, healthy battery.

Kev

 

[darsben]

Charge it up. Take it out. Go to auto parts store and have it load tested.
Then you know we can only guess

 

[bigfatguy]

I'll combine the various replies into one post to save time.

The batteries are AGM, and there are two in parallel, but they are each smaller than the Sprinter's starting battery. I've read some reviews of this rig, and basically everyone agrees that it's battery capacity is a serious weakness... so it looks like an upgrade to lithium is in the works.

The rig is about 13 months old now, and we have run the house batteries down to failure a couple of times.

The batteries were load-tested at the service center (they are mounted in a horrible place for self-service, unless one happens to be a yoga expert, and not a Big Fat Guy...) and they passed, but he warned they were at the lower-end of passing, and would need replacement "sometime soon".

I'm just trying to decide if I need to replace them TODAY, with a trip planned this weekend. I think we'll be good.

Thanks, all!

 

[Alfa38User]

..... and we have run the house batteries down to failure a couple of times.

And herein lies the root of the early failure!! I am not sure for the exact % for an AGM battery but the so-called "deep discharge" lead-acid batteries should NOT be discharged more than 50% or so. You are living the result of such a practice.

You may be in for a shock once you price lithium batteries in that size range.

 

[Gary RV_Wizard]

You said the batteries are physically smaller than the starting battery?  What is their case size and amp-hour capacity?  From what I can see in the Winnie Era brochure, it should have two Group 31 size AGM batteries, and those aren't small!  Or short on AH capacity (about 130 AH EACH).  Many much larger rigs have less!

 

[bigfatguy]

And herein lies the root of the early failure!!

in my defense, this is our first RV, and we simply hadn't gotten a routine together for boondocking.

You may be in for a shock once you price lithium batteries in that size range.

No doubt.

You said the batteries are physically smaller than the starting battery?

That's based on me eye-balling the house batteries from a somewhat non-optimal position (both batteries in the house are a real PITA to lay hands on), but, yes, they do seem to be smaller than the rig's.

  What is their case size and amp-hour capacity?

at some point, I'll have to jack the rig up and crawl underneath to find out the specifics. Now that I think about it, I do have a selfie stick somewhere...

  From what I can see in the Winnie Era brochure, it should have two Group 31 size AGM batteries, and those aren't small!  Or short on AH capacity (about 130 AH EACH).  Many much larger rigs have less!

Do you have a link to the document you found that reference in? I've been trying to find specifics about the batteries in the documentation and the parts-finder tools, but haven't had any luck yet.

 

[KandT]

Hey big fat guy. Welcome to the forum.
Love the name!

At first I was like "Whoah there Jeff. This is the friendliest site on earth."  Then I realized the name.

Best. Name. Ever.

Now on to the batteries.  Yeah mine go down fairly quickly on voltage.  I suspect they are going bad BUT I don't boon dock unless it is in a crappy parking spot.  Preferably one with Diesels coming in and out all night.  So I figure I will go until they won't goes no more.

If you see a big voltage drop while you are connected to shore power you may have a converter (charger) issue.  Correct me please if I am wrong on this one but I believe the RV equipment is generally run off the batts but while on shore power the converter will replace the charge about as fast as the rig depletes it.  Therefore the batts stay about even. 

I should change my name to "BecomingBigFatGuy"

 

[bigfatguy]

The rig works great when connected to shore power. It's got a surprisingly good charger for an off-the-rack model: an inteli-Power 9200 (? I think I got that right).

Problem is, about the only place this rig gets plugged in is at home between trips. We avoid full-service parks on purpose.