AGM Battery Useage

[66lincoln]

Hello,

I'm a new owner. I'm looking for some pointers on understanding my battery usage.
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System:
Two Renogy AGM 13V, 100Ah each batteries wired in parallel. I understand this produces a system of 13V, 200Ah of which only 50% at best is useable (100Ah).
Renogy ADM500 Battery Monitor
GoPower 100W solar panel with controller (factory installed)
LIFEPO3 batteries are on my list, but not until next year.
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Parasitic Draw of about 0.3A from:
Refrigerator
LP detector
GoPower controller (when not receiving sunlight to keep the display active)
Any trace current the power center is using as the LP detector is live.
Furnace was off as it was 60 degrees at night and 80 degrees during the day.
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Trailer:
2022 212QBW
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We've taken just two, two-day weekend trips with the trailer. The first trip all we had was the standard Jayco battery monitor which is nothing more than a series of LEDs to guestimate the battery level.

The second trip we had the better battery monitor.

On the second trip, Night #1, we started the night at 13V and 100Ah (100%). We watched a movie that was about two hours long. The monitor showed 1.1A during that time period. Then I ran my CPAP for the next about 8 hours. The monitor showed 0.8A to 1.2A depending on if I was inhaling or exhaling. We'll just use the higher constant of 1.2A. (Note, the amp reading on the monitor is inclusive of all parasitic draws; LP detector, fridge etc).

The total should be 11.8Ah or equal to 88% of the 100Ah available. 12.6V was the ending voltage. Which makes sense as according to Renogy's chart, 90% is 12.75V and 80% is 12.5V.

Night #2. Same starting situation as Night #1. Except, in the morning the voltage was 12.2V. Renogy's chart shows 12.05V is 50%. On Renogy's chart, 12.2V equates to about 65%. That's 13% lower than Night #1. Day #2 was all rain and so the solar panel was ineffective, a gas generator was used to supply power to the trailer's systems to recharge the batteries prior to turning on tv.
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Questions:
1. Why was Night #2 so draining on the batteries? 45% of 100Ah in one night seems excessive.
2. I expected to run the trailer for two days without any need for substantial charging; just some trickle charging from the solar panel during the day.
3. At the start of Night #2, I suspect the batteries were not to full charge. While the monitor stated 13V and 100%, the charger was still supplying 4A which was down from 9A. Am I correct is suspecting the 13V and 100% reading is unreliable until the charging amps drops to float/minimal?

[craigav]

The primary reason for what you are seeing is that the battery voltage is unreliable for determining the state of charge whenever charging or discharging a battery(s). The voltage is a good indicator when the battery has not been charged or discharged any (resting voltage) for around 4~6 hours. There are other meters that can more precisely determine the state of charge by monitoring the current going in and out of the battery bank, and something you likely would find of value especially with LifePo4 batteries. ~CA

[RogerR]

One of the advantages of the Renogy bluetooth Lithium battery and Renogy MPPT is that you can get exact state of charge and charge rate via bluetooth to your phone.

You can also get a shunt which measures battery amps in and out, read some posts or watch youtubes on how they work.

One catch on the Renogy app is that it won't work unless you log on before leaving cell signal or wifi connection. If boondocking really off the grid it is problem.

If you go Renogy make sure you contact a Renogy owner as they can get you an extra 7 % off unless Renogy changes the rules.

My 100 amp battery and 200 watts of solar stayed full every day and coasted through the snowy nights this spring in Great Sand Dunes NP. Full by 1 pm even in cloudy weather!
Since you already have a great battery setup I would suggest adding 200 watts of solar and a mppt controller. Your current wiring should be good enough if it is #10 down from the solar panel you have.

[EJH]

I have similar to RogerR's setup with a single 100AH Bluetooth Renogy lithium, bluetooth Renogy MPPT 30A charge controller and 390W of solar panels (190W Go Power stock panel plus 200W Rich Solar panel, wired in series).

We dried camped for 4 nights in NW Washington, with little sun except for one day which did a good job of charging the battery close to 100%. Other cloudy days only charged about 10-15 AHs

We have a propane fridge.
We watch about one hour of TV (32" 12v tv with a Roku stick).
We used the furnace to heat from about 50 degrees outside to 65 degrees inside.
We ran the water pump and interior lights as needed, plus charged cell phones.

We averaged 25-40 AH of usage from evening to morning (about 16 hours, say 5pm to 9am). The 40AH was a very rainy day where we were inside an extra few hours, with lights, furnace, etc on.

I think you are under calculating your usage. 11.8AH over night seems way low with what you are powering. You really need a good shunt meter, or a bluetooth battery with built in monitoring.


Edit, your Renogy ADM500 Battery Monitor should work as a battery shunt monitor and tell you exactly how many AHs you are using and the exact state of your battery's charge....is it setup correctly?

[66lincoln]

Yes, my Renogy monitor is a shunt monitor and it is connected correctly according to the instructions; double and tripple checked.

All of my Ah readings, voltage and percentage were taken directly from this device. It does tell me amps out (-) and amps in (+).

On the rainy day, the panel only produced 0.1 to 0.3 amps at any given time all day. But that's not the issue as it was supplemented with generator.

I guess my confusion is why the monitor states 100% when the charger is still pushing 4+ amps into the battery (which I can see on the monitor) which to me seems to indicate the battery isn't fully charged and hence I may be shutting off the charger too soon.

[EJH]

Sounds like your Renogy shunt meter is not calibrated properly. You need to charge the battery 100%. Know the battery is fully charged, then tell the meter the battery is at 100%. You also need to set the meter for the battery capacity. I would keep charging the battery until it no longer takes any current, then reset the Renergy meter to 100%.

[dvspl]

Even though you've double and triple checked the way the shunt is connected, something still seems wrong there. 1.1 A at 13 V (less than 15W) seems way too low for a TV and whatever device (bluray player, etc) was playing your movie. My 32" TV uses 60W (~5 amps) by itself. I don't have a shunt based monitor, but from what I've read on here, the most common issue is that ALL grounds don't go through the shunt. Seems like something is not being read.

[EJH]

Originally Posted by dvspl

My 32" TV uses 60W (~5 amps) by itself.

My 32" Connexion 12V TV will use 1.5 amps on TV (antenna) in power save (very low back-lighting, almost unusable). In normal back-lighting (standard), it uses 2.5 amps. I measued this with a meter at the battery turning the TV on/off and checking the current draw change.

1.1A for a TV, unless very small and low back-lighting, seems very low to me. However, ~5A also seems high to me.