Is it OK to keep a battery tender plugged into the t@b's exterior 110V plug when on shore power?

Campwise

At a campground that offered both 30V and 110V plug-ins on the pedestal, I kept a battery tender plugged in for days to maintain charge on my 6V batteries.  It was great not to worry about them.  If, as is more typical, only 30V and/or 50V is on a pedestal, would it overtax the t@b's electrical system to keep a battery tender plugged into the exterior 110V plug for several days at a time?  Thanks in advance for sharing your insight and wisdom ;~) 

N7SHG_Ham

Should be ok, just remember that total draw to the camper can't exceed 30a and the battery tender would take capacity away from whatever else you want to use on that circuit.

Sharon_is_SAM

You mean 30 or 50 amp and 110 v.  My battery tender specifically states to not apply a load to the battery while charging.  Although you are operating on shorepower, are you turning the battery switch off or are you charging via the converter and tender simultaneously?  Why not just use the converter?  What battery do you have?

Campwise

Oops!  Still learning - I meant 30 or 50 amps.  I have dual 6V Crown CR-220 commercial deep cycle batteries.  If I can plug in the battery tender while connected to 30A (or less often 50A) to keep them charged, I won't have to listen to the converter cycle on/off, and I've read they don't do a great job keeping the batteries charged.  Yes? No?  When on shore power, and any time using the tender, I turn the t@b battery switch off.  I use a Battery Tender Jr. 12V, 750mA output current.  Set me straight, please, if my proposal isn't a good or safe one.  Thanks!   

VictoriaP

Unless you have lithium batteries, which prefer a higher charging voltage, the converter does a fine job of charging. The only reason I can think of to use a separate charger is to rescue deeply discharged batteries or if you want to top off with a generator (still not really necessary as you can use the 30 amp cable with an adapter as needed.) And if I’m doing either of those, I’d use a much, much better charger than the one you have for either of those jobs.

Your battery tender jr is basically a trickle charger. If your batteries were at all depleted, it would be unable to charge them according to the manufacturer’s own specs, which say it can only really charge a small battery of the kind you’d find in a motorcycle, for larger batteries, it simply maintains a charge. Given that you turn your disconnect to off while plugged in, there’s no drain and nothing to maintain. 

Additionally, your converter should only be running the fan occasionally under normal circumstances. 

I’m just not seeing any advantage here. You’re not hurting the battery, but you’re not going to see any real benefit either as far as I can tell.

N7SHG_Ham

Would recommend just letting converter do the job it was designed to. At 3/4 of an amp output from battery tender, any use at all will be beyond the ability of the battery tender to keep up. That is made more for long term storage once a battery is fully charged

pthomas745

"When on shore power, and any time using the tender, I turn the t@b battery switch off."

How is the battery tender or the shore power charging the battery with the battery switch off?

Sharon_is_SAM

@pthomas745 - Campwise plugs the battery tender into the TaB 110 v outlet and I assume uses the alligator clips on the battery terminals.  You can charge the battery via a tender with the battery switch turned off.  

@Campwise - Crown makes some very good batteries.  I can see why you want to protect your investment.  There has been a discussion on the forum regarding how some AGM batteries are not fully charged as the converter does not stay in the bulk vs absorption phase long enough.  We charge our AGM via a battery charger before storage for this reason.  However, that does not necessarily apply to your batteries.  You need to check your battery charging parameters to know for sure.  And as VictoriaP noted - you may not be accomplishing what you intend using your tender.  What battery monitor are you using?

Here are your battery specs.
https://cdn.shopify.com/s/files/1/1579/5179/files/CR-220_PowerSheet_D06220_0213.pdf?16021135676618962151

Campwise

This is becoming more clear.  I didn't know that when the battery switch is on off, there's "no drain and nothing to maintain" - I assume that means for up to 4 weeks at a time for lead acid batteries.  And I didn't know the trickle charger (that at home I always have attached via a solar port) can't bring a battery back to full charge if depleted. 

To monitor the batteries, I use an Adventurer charge controller that's installed inside the t@b - it came with a Renogy 100W suitcase panel.  I carry an electric meter in the toolkit, but haven't used it.  Probably should! 

It sounds like allowing the converter to do it's job, to both bring the batteries back to full charge and keep them charged, is the way to go. 

I treat the 6V's like twin newborns in need of tender loving care to survive.  True to some degree, but it's time to let them shine.  We take our first week-long boondocking trip in September.   Thanks to all for your thoughtful input.

pthomas745

@Sharon_is_SAM AHA....I should never post on technical matters at 4:30 AM.......

Sharon_is_SAM

@pthomas745 - at least not until you have caffeinated😜

VictoriaP

@Campwise So, I have a single 105ah AGM on my 320. It’s now over a year old, and it’s mostly been charged via the converter. Since I was installing a quick disconnect pigtail on it this week for my portable solar, I decided it was also time to learn to use my multimeter instead of relying on the 12v plug in I use inside the trailer. After a full charge via the converter, I switched the battery disconnect to off and waited a full day to check the battery. Multimeter read 12.9...exactly correct for a fully charged battery of this kind per the manufacturer’s specs. The converter is obviously doing its job just fine with my battery. Test yours the same way: charge the batteries via the converter for a couple of days, shut them down for at least a full day, then measure. Search the manufacturer’s site for the specs and compare. Then you’ll know for certain whether your converter can charge your batteries.

That said: At a minimum, replace that tiny battery tender with one adequate to the battery size. My recommendation, get a NOCO Genius if you want a good charger, and given the size of those batteries, make it a Genius 10 or larger. It will be capable of fully charging a depleted battery (not simply maintaining it), it can help repair damaged cells as needed, and as a smart charger, it will charge appropriately to keep your batteries in good working order. Works on 6v, 12v, and lithium. An adapter is available to use with your solar port, I bought one this week for the pigtail I installed. I have an older Genius I use on my car routinely, since modern cars often have a higher than you’d expect amount of parasitic drain, and it’s done a terrific job of preserving my expensive Optima deep cycle for years on a car that sits way way more than it drives. I wouldn’t hesitate to use it on the trailer battery if I needed to, in fact, I put the 30 amp cable away this week, shut the battery off, and am going to just check the battery every month or two this winter. If it needs topping up, I’ll probably use the Genius to do so as the parking situation leaves the trailer’s 30 amp socket a little awkward to get to, and I’m tired of tripping over that big cable.

Campwise

We only know what we know when we know it.  Thanks so much for updating my understanding.  I ordered a NOCO Genius 10, and look forward to improved battery care  

VictoriaP

Campwise said:

We only know what we know when we know it.  Thanks so much for updating my understanding.  I ordered a NOCO Genius 10, and look forward to improved battery care  

I think you’ll be pleased with the NOCO, several people here have them as well. Here’s the link for the adapter to use with your solar port: https://smile.amazon.com/gp/product/B005DUMADC/ Double check the polarity before first use, I don’t have the Zamp port and matched my pigtail appropriately, but I understand the Zamp port often requires a reverse polarity adapter when using non Zamp accessories.

I also have their OBD II adapter for use with my car. While using the provided alligator clips is fine, I like the convenience of having quick connects where possible.