Question on Battery Life

[GSP9]

Last fall we bought a 2013 25' International that we bought from the original owners. It came from the factory with two 80 watt solar panels. The original owner was a pretty meticulous guy and always stored the batteries inside on a float charger during the winter (Pennsylvania). I did the same this past winter and reinstalled them about a month ago. I'm a pretty handy guy but batteries and electrical are not my strong point. The solar seems to have no problem recharging the batteries after minimal use. But, I noticed that when the control panel has the batteries at 100%, as soon as I turn on a few of the lights (LED) the % remaining quickly drops to 80-85%. It tends to be a fairly slow drop after that. As an example, walked in the other night and it was 100%. Turned on a few lights and it dropped to 85%. Put a movie in and watched on both tv's. After the movie was over (2 hours) it was jumping between 65-70%.

My question is, is the initial drop of say 15% from 100% down to 85% a result of the batteries being 5 years old? If I were to put two new batteries in would it drop to maybe 95% after turning a few lights on? I'm trying to wrap my head around exactly how the batteries are being drawn down before we head out on some trips this summer.

[sgschwend]

For me the best way to see how healthy the batteries are is to load test them. It isn't that difficult but you would want to graph the battery voltage and current draw overtime.

Many users use a Victron battery monitor or similar device to do this and compare the power delivered versus the battery size. The monitor would be added to the trailer. Perhaps your system has this type of device and you could charge your batteries, reset the watt meter then run an average load.

As to battery usage: lead acid batteries need to be kept above 50% charge. Therefore two 100 amp hour batteries should deliver 100 Ah the power is the average voltage time the average current.

[PKI]

Batteries degrade with use, but what you are seeing is that a battery with no load will read X volts. When a load is applied it will read less.

The question is, are your batteries degraded enough to not be usable for your application? Was the consumption more than the capacity in your current batteries. If so, you need to replace or upgrade. Obviously, the bank is usable if you limit the consumption amp hours.

Five years on wet cells = time to replace in the world of preventive maintenance. Five years on AGM cells = should have more time, but they can be damaged by too many over 50% draw downs. Magic banks can discharge lower but cost a premium to purchase and install.

Lesson is - determine consumption budget and work within it or upgrade. Step one might be best to research battery monitors. Sounds like yours is helpful, but there are likely better. Might be worth researching. The right monitor should give you the answer you asked. However, a pair of Walmart wet cells is about $200 and may best cost effective investment. How to manage your power has many different tactics. Go with what is right for you and your RV lifestyle. Pat

[AirMiles]

I noticed that when the control panel has the batteries at 100%, as soon as I turn on a few of the lights (LED) the % remaining quickly drops to 80-85%. It tends to be a fairly slow drop after that. As an example, walked in the other night and it was 100%. Turned on a few lights and it dropped to 85%. Put a movie in and watched on both tv's. After the movie was over (2 hours) it was jumping between 65-70%.

I don't think an "initial" drop to 85% is abnormal. I did a 10 Amp load test on two brand new deep cycle GC2 batteries and they functioned very similarly to your old batteries. Fully charged, well rested, and with no load, my new batteries read 12.72 Volts. Immediately upon turning on a 10 Amp load they dropped to 12.4 Volts. Your two TV's, a DVR, plus the Inverter is probably close to a 10 Amp load. If your monitor is using "Volts" to determine your battery status, likely, your load would be enough to drop the status to 85%.

For the next several hours at a 10 Amp load, my new batteries slowly drop by 0.01 Volt per hour. This is similar to your "slow after that" comment. After six hours, my batteries start dropping at a faster 0.07 Volts per hour. At that point, I rested the batteries for an hour, retested the voltage, and "presto" that 0.3 Volts that immediately disappeared under the initial load re-appeared with no load. I'd bet your battery would recover similarly with no load. I then recharged my batteries and considered my load test a success.

The bottom line in all of the above is that even my brand new batteries lost 0.3 volts immediately under a 10 Amp load. As others suggested, I would continue using your old batteries until they do not provide enough power for a full night of boondocking before I would replace them.

[waninae39]

yes, get a Victron battery monitor
it can show you how the battery is working over time

[GSP9]

Lots of good info. Thanks for the replies.

[jnm30327]

A Victron monitor is a life saver. Highly recommended.

Another item that is helpful is a kill switch on the battery. The parasitic loads on a Airstream even in storage mode are more than you might think. These loads are enough to pull a fully charged set of batteries down to 50% within a couple of weeks.

[Martee]

Originally Posted by GSP9

Last fall we bought a 2013 25' International that we bought from the original owners. It came from the factory with two 80 watt solar panels. The original owner was a pretty meticulous guy and always stored the batteries inside on a float charger during the winter (Pennsylvania). I did the same this past winter and reinstalled them about a month ago. I'm a pretty handy guy but batteries and electrical are not my strong point. The solar seems to have no problem recharging the batteries after minimal use. But, I noticed that when the control panel has the batteries at 100%, as soon as I turn on a few of the lights (LED) the % remaining quickly drops to 80-85%. It tends to be a fairly slow drop after that. As an example, walked in the other night and it was 100%. Turned on a few lights and it dropped to 85%. Put a movie in and watched on both tv's. After the movie was over (2 hours) it was jumping between 65-70%.

My question is, is the initial drop of say 15% from 100% down to 85% a result of the batteries being 5 years old? If I were to put two new batteries in would it drop to maybe 95% after turning a few lights on? I'm trying to wrap my head around exactly how the batteries are being drawn down before we head out on some trips this summer.

My 2018 25FB with 160 watt Zamp Solar also does the same. Shows 100% Battery on entering, and then turn inverter switch on and immediately shows 95% and after 2 hours shows 85%. The load drain on battery appears normal...and gets back up to 100% battery with just 4 hrs of sunny weather.

[GSP9]

Learned an interesting lesson on solar over the weekend. We finally have some nice weather here in PA with sunny days and temps in the 60's. Sunday my daughter wanted to watch movies in the trailer so I opened it up and it was pretty warm in there as the sun was directly overhead. Turned on one of the fans, put the movie in and she watched on the tv. I walked back in about 15 minutes later and the panel indicated it was still 100%. After about 30-35 minutes it finally dropped to 95% and by the time she was done a few hours later, it was 90% and I think she had one of the lights on too.

During previous usage with the batteries, it was either cloudy or evening. I guess in my mind I always knew the batteries would do better with the sun out but didn't think it would be that much better. Anyways, made me feel better about how to manage battery power based upon sunshine, cloudy, or night time.

[xisme2]

This answered a question of mine, with the factory kill switch off the parasitic loads would be enough to pretty well flatten 2 new batteries in a 2018 Globetrotter. My dealer told me that "only" the gas monitor was upstream of the cutoff, but I read somewhere here that the inverter in normal mode and the sub woofer are also on.

[Mattirs]

Originally Posted by GSP9

Learned an interesting lesson on solar over the weekend. We finally have some nice weather here in PA with sunny days and temps in the 60's.

During previous usage with the batteries, it was either cloudy or evening. I guess in my mind I always knew the batteries would do better with the sun out but didn't think it would be that much better. Anyways, made me feel better about how to manage battery power based upon sunshine, cloudy, or night time.

Most controllers, up to its capacity, will put out as many amps as the system will is drawing. This way, especially after the batteries are fully charged, you do not need to worry about moderate power draws during sunny days. On warm sunny days you 200W or more will easily keep up with your fans in the middle settings. My 200W homebrew kit kept up with all the led lights and the Fantastic fans on.[emoji2]