Solar/Battery power needs calculation

Please correct my calculation errors as needed. We recently acquired a solar panel and are trying to figure out how to be sure we use the setup in a way that doesn't damage or shorten the life of our trailer battery.

Our 2008 550 Ultra came with a smaller 34ah or so battery. CampInn recently installed the larger battery, which I think is an 80ah...? Also added the port to connect the solar panel.

Assuming the new battery is actually 80ah, I've read and seen here that you should use no more than 50% of that capacity to avoid shortening the battery life. So, 40ah is available for use.

We also just bought the Dometic, which is rated at 45W, or 3.75A. If the Dometic runs 15 minutes per hour that would = .9375A. I'd probably assume a 1.5A rate to be conservative. 1.5A X 24 hours = 36ah

Lights @ 1A X 3 hours = 3ah
Phone chargers @ 2A X 4 hours = 8ah
Water pump @ 2.5A X .2 hours = .5ah

That totals 47.5ah, which exceeds the available 40ah.

The solar panel, a Zamp 120W portable kit, is rated at 6.84A. At 8 hours of input that = 54.72ah. Assuming 70-75% efficiency, that adds about 40ah back to the battery.

Am I correct in assuming that I will net out with a 7.5ah deficit per day? Which would give me just over 5 days (40ah of usable battery power / 7.5ah deficit per day = 5.33 days) of battery use before needing to either run the tow vehicle or connect to shore power?

 

Thanks Al, all good suggestions. Except the Yeti... we're already too spoiled by the Dometic.

 

We still have limited experience with the solar panel. On this trip we've only used it 2 day, and they weren't back to backs. It worked well, but that really isn't enough use to determine if it can handle our needs on an extended basis.