Solar trickle charger

[MURPHY55347]

So I'm using a Battery Minder 20 watt solar panel to keep the batteries topped off. I'm tying to figure out if it's working correctly. It's partly cloudy today and I'm reading 13.25 volts from the solar panel going into the controller. But coming out of the controller and going to the batteries I'm reading 12.5 volts which is exactly what the batteries are reading. Coming out of the controller I'm using a splitter with one leg going to the starter battery and the other is connected to the both of the coach batteries. Battery Minder says I should be able to charge 4 batteries. The starter battery is completely isolated using a manual battery disconnect. This is a class A motorhome. It just doesn't seem like there is enough oomph to do the job. The other issue I'm dealing with is I'm questioning the integrity of the batteries. We purchased this motorhome new last May and I know it probably sat on the lot for a year before we bought it. Stater battery for one just doesn't seem to want to hold a charge but in the same breath I'm not sure the solar panel is doing its job. It's the middle of winter here so not much fun trying to do anything with it being cold out. I know I should have the battery tested but the other 2 batteries have to come out first and the starter battery weighs 46 pounds which is difficult for me to handle.
So to sum it up I have 2 questions.
Is the solar panel working correctly?
Can all the batteries be toast having been probably sitting in an uncharged state?

[time2roll]

For best results the battery needs to be fully charged and disconnected for this trickle maintainer. Will do much better in the summer.
12.5 is not full charge.

[2oldman]

MURPHY55347 wrote:
It's partly cloudy today and I'm reading 13.25 volts from the solar panel going into the controller.

Voltage doesn't tell you much from a panel, but it should be more than 13.

As said, a 20w panel is not enough.

[pianotuna]

Minimum 60 watts per 100 amp-hours of storage for solar. With flooded, about 150 watts maximum per 100 amp-hours.

This series of articles may help: https://freecampsites.net/adding-solar/

[All_I_could_aff]

20 watts max= less than that most of the time, which means not enough. And remember, parasitic loads suck power 24 hours a day, sunny or cloudy.

[azrving]

Wet cells? Check the specific gravity and as mentioned more panel

[FLY_4_FUN]

Depending on the parasitic loads that your rig has...I doubt that 20W will keep things charged on anything but perfectly sunny days in winter. The angle of the sun is too shallow and modern rigs have items consuming 12V more so than 10-20 years ago. I would first check the fluid levels in the batteries and disconnect them from loads if able. I don't want to call a 20W panel useless...but most folks who toss a tiny panel on their dash find out fast its just not enough. I like to bring my batts indoors and put on a Deltran Battery Tender as needed in winter.

[time2roll]

For the conditions and equipment I would say most likely everything is working fine.
Really need 100+ watts. Battery at 12.5 is fine but OK to put a charger on if you are concerned.

[MrWizard]

20watts, even at max output full sun thats pretty small
right now you are probably getting less than 10watts

thats about 0.8 amps AKA 800ma to try an maintain your 3 batteries ?

i think thats a loosing situation, batteries are going to go down
as you are finding out

[Lwiddis]

Twenty watts on a solar setup for four batteries seems too light to me. I use 30 solar watts on two Trojan T125s to keep them at 12.7.