Battery Not Charging on Tender

That battery tender is only going to put 18 ah max in a battery in 24 hours.
Give it a week or so and the batterys may be charged.

Good maintainer. Too small to actually charge a low battery. I think they time out in 72 hours so on the fourth day disconnect and restart them.

Didn’t the instruction booklet cover this? Tender vs. charger?

Thanks for the advice. The batteries shouldn't have been THAT low, I wouldn't think. From a new trailer that we had taken out once (so possibly a bit depleted) that have been disconnected from the trailer and stored indoors for about a month and a half - two months.

I guess I'll give it more time and disconnect it in a few days.

Batteries need to be in "good" condition to begin with. That means at least 12.2 volts for any kind of maintainer.

Self discharge takes place even when not hooked up to your RV, and temperature and age can excellerate self discharge. Monitor the voltage, don’t guess. It will lengthen your batteries’ life. “Taken out once” could have used 20 to 30 amps on parasitic loads alone depending on how many days you were out.

oyarsa wrote:
It's been a couple of days, though, and it's still just a solid red. Shouldn't it be charged by now?

No, it may not be fully charged if the batteries are low.
Battery tender chargers are low amp chargers.... VERY low amp.

Not unusual if the battery has lost a good amount of charge. The junior's are very slow chargers as they only supply 0.75A to the battery. If a battery is low it will take days for it to reach just 80%.

Are the batteries disconnected from the coach?? There is parisitic draws from many things inside, radio, CO detector, thermostate, fridge, etc... These draws most likely exceed the output of the tenders. Since you have power to the rig, just plug it in and use the convertor to maintain the batteries, that is what it is designed to do.

As said, the battery tenders are designed to just keep a battery topped off. They will charge the battery but very slowly. If you are looking for more of a charger with tender capabilities, check out ctek chargers. You want a 10 amp charger for a single battery.