Rapid battery decline

kipwill · October 8

In the past we had occasional problems keeping the battery strong in our TAB, but after replacing the original lead/acid battery with a LiTime lithium battery last year we've been able to camp without shore power for about 3 days and have our fridge, etc. still operate. (We also have 2 small solar panels on the roof.)

But this week, just as we are about to leave for a long trip, we noticed the CO/propane monitor was flashing and buzzing. Based on comments previously posted in this forum, a low battery seemed like a likely cause. So I plugged into shore power overnight, and everything seemed normal the next day, even after disconnecting shore power.

I began checking battery level on our wall monitor after that, however, and noticed that the battery reading dropped from 13.0 to 11.9 over about 2 days, with no major users (fridge, heat, etc.) turned on. Then when I checked it this morning, the monitor wouldn't even light up when I pressed the battery button, and the CO/propane monitor was again flashing alarms. I once again connected to shore power at our house, and the battery measured 13.6. I disconnected shore power after a few minutes to check battery level, and got a 13.0 reading without shore power. I now have shore power hooked up again, just to make sure we have the battery fully charged.

My problem is that I can't figure out what I can do to be allow us to start our trip and be able to count on the battery retaining a strong charge. (BTW, the on/off switch near the battery on the tongue is turned to green.)

Does anyone have a suggested remedy?

Thanks in advance,
-Will

kipwill · October 8

P. S. In next-to-last paragraph I should have said "I disconnected shore power after about 90 minutes to check battery level, and got a 13.0 reading without shore power."

webers3 · October 8

The easiest thing to check is the emergency brake pin at the end of the cable that you attache to the tow vehicle, to be sure it's not out, which would engage the trailer brake and drain the battery. After that you need to use the multimeter to try do find out where the current draw is coming from

Marceline · October 8

kipwill said:

In the past we had occasional problems keeping the battery strong in our TAB, but after replacing the original lead/acid battery with a LiTime lithium battery last year we've been able to camp without shore power for about 3 days and have our fridge, etc. still operate. (We also have 2 small solar panels on the roof.)

But this week, just as we are about to leave for a long trip, we noticed the CO/propane monitor was flashing and buzzing. Based on comments previously posted in this forum, a low battery seemed like a likely cause. So I plugged into shore power overnight, and everything seemed normal the next day, even after disconnecting shore power.

First, you should turn off the battery switch when your camper is parked and not in use, especially if your solar panels are covered. Second, plugging into shore power overnight may not have been sufficient to fully recharge a completely depleted battery. If you don't have a lithium-compatible converter in your trailer, you may need to get an external charger that is capable fully charging a lithium battery. You don't say the year of your T@B but the original converters can only charge a lithium battery to about 80-85%. Or you need to get your trailer into full sun for a few days. Be sure that your solar controller is set for a lithium battery.

I began checking battery level on our wall monitor after that, however, and noticed that the battery reading dropped from 13.0 to 11.9 over about 2 days, with no major users (fridge, heat, etc.) turned on. Then when I checked it this morning, the monitor wouldn't even light up when I pressed the battery button, and the CO/propane monitor was again flashing alarms. I once again connected to shore power at our house, and the battery measured 13.6. I disconnected shore power after a few minutes to check battery level, and got a 13.0 reading without shore power. I now have shore power hooked up again, just to make sure we have the battery fully charged.

My problem is that I can't figure out what I can do to be allow us to start our trip and be able to count on the battery retaining a strong charge. (BTW, the on/off switch near the battery on the tongue is turned to green.)

Does anyone have a suggested remedy?

Thanks in advance,
-Will

13.0v is actually a very low voltage level for a lithium battery, so your battery wasn't fully charged to begin with. The monitor on the wall is barely reliable for lead acid batteries and is not reliable at all for a lithium battery. If you do a lot of off-the-grid camping, I recommend you install a Victron SmartShunt, which measures amps going in and out of a battery. The measure of 13.6v when you connected to shore power isn't a measure of the battery level, it reflects the current going into the battery for the shore power.
My recommendation to get you on your way for your trip: Buy a lithium-compatible battery external charger and connect it to your battery to get it fully charged. If you have a 100aH battery and you buy a charger that outputs 10A you will need to leave it plugged in for at least 10-12 hours. If you buy a charger that outputs 5A you will need to leave it plugged in twice as long.

kipwill · October 8

Thank you both for your comments. We are not hooked up to TV via 7-wire at present.

As for the battery switch, we have been unsure when to turn it off (red). It sounds like any time we aren't using the camper and won't have solar gain we should turn it off, but leave it on (green) if our solar panels will be helping keep the battery charged. Is that accurate?

Marceline, I did set the solar controller to lithium when I installed the new battery last year.

Li Time, the lithium battery manufacturer, has an app that measures battery charge via BlueTooth. I've read it is much more accurate than the NuCamp wall monitor, especially for a lithium battery. At present, after being on shore power for over 4 hours, the app tells me we are at 99% SOC.

So that still leaves me with the question of why the battery became so depleted. Fridge is off, not using heater or even LED lights, not connected to tow vehicle. What would you suggest?

pthomas745 · October 8

You don't tell us what year your trailer is, or if you have a better battery monitor than the "blinky light" model in the trailer.

Tell us the year and model of the trailer. And: a multimeter would be easy to get and be a much better source of info for your battery.

Marceline · October 8

kipwill said:

Thank you both for your comments. We are not hooked up to TV via 7-wire at present.

As for the battery switch, we have been unsure when to turn it off (red). It sounds like any time we aren't using the camper and won't have solar gain we should turn it off, but leave it on (green) if our solar panels will be helping keep the battery charged. Is that accurate?

Marceline, I did set the solar controller to lithium when I installed the new battery last year.

Li Time, the lithium battery manufacturer, has an app that measures battery charge via BlueTooth. I've read it is much more accurate than the NuCamp wall monitor, especially for a lithium battery. At present, after being on shore power for over 4 hours, the app tells me we are at 99% SOC.

So that still leaves me with the question of why the battery became so depleted. Fridge is off, not using heater or even LED lights, not connected to tow vehicle. What would you suggest?

I confess that I don't remember what the converter output is, but 'm skeptical that your battery is really at 99% after four hours plugged into shore power.

You should turn the battery switch off (red) when the camper is parked, not connected to shore power, and not being used. There's no reason to keep it on. The phantom drains from items like the CO/Propane detector, TV, radio will just slowly drain the battery. The solar panel wiring should not go through the switch, so the solar should charge even if the switch is off.

You don't say how long you left the trailer parked with the switch on, but most likely the battery was just slowly draining as long as you had it parked, and the measures you've taken since have been insufficient to get it fully recharged.

kipwill · October 9

I'm sorry I omitted some basic info. Our camper is a 2018 CS-S.

I'm not sure what the the "blinky light" model in the trailer refers to. We have a wall-mounted monitor that gives numbers for battery, gray water, black water, etc. It sounds like that data is not a reliable source of information on the level of battery charge, especially with a lithium battery.

I understand that our T@B converter can only charge a lithium battery to about 80-85%, but with our solar panels or shore power we have been able to get close to fully charged.

Tonight we are plugged into shore power, and we'll see what the situation is in the morning. The challenge in doing so is that many people say the Nu Camp wall monitor does not accurately report the state of charge for a lithium battery, while some other don't trust the app offered by Li Time to give an accurate report on battery state of charge. It's hard to evaluate which argument to accept.

We have had our TAB 320-SCS parked near our house for about 3 weeks without being plugged into shore power. We've done that for similar periods in the past year without having he CO/Propane monitor go into alert mode, or the battery decline significantly. Maybe our current parking spot is more shaded in terms of solar panels keeping the battery well charged? I'm not sure what else might be fundamentally different.

If we are truly using battery power in some way that we're not aware of, I'm not sure how to chase that down. Would I need to buy a clamp meter and check every place that electricity might be getting used?

Grumpy_G · October 9

Ignore whatever external gizmo you have and only use the information the battery provides. The BMS has much more detailed data, typically down to the voltage of individual cells. I helped a friend with his LiTime battery a while ago and if I remember correctly the app does show charge/discharge state and the actual current going in or out. The latter is useful for troubleshooting: turn off the battery switch and outgoing current should drop to zero. With the battery switch on, solar disconnected, shore power disconnected, pull and reinsert the individual 12V fuses in the "power center" one by one and look for a change in discharge current. Also, as already suggested check the emergency brake pin as an activated emergency brake will drain the battery in short time.

Sharon_is_SAM · October 9

Do you have an inverter?

pthomas745 · October 9

In your 2018, you have the SeeLevel Monitor. (I have the same one in my 2017). For many reasons, these monitors for any battery are extremely misleading. Since these monitors for battery voltage only seem to know how to measure a "lead acid" battery, that is all they know. They cannot measure any value higher than 13.6, it seems. The best/accurate/reliable monitors will be the Victron shunts or solar controllers, or any battery device connected directly to the battery. Even a multimeter, properly used, will be more accurate than the SeeLevel.

I still have not been able to figure out what these "bluetooth" apps from the battery are actually measuring, or how they measure it. They appear to cause more confusion than useful data, especially when the Victron devices and the "battery app" somehow do not agree. If they are simple voltmeters, then in every case, a Victron shunt will be more accurate.

The battery switch should be "off" when you aren't going to be using the trailer. With the battery switch off, and solar connected directly to the battery, the solar will still charge the battery "when" it needs to be charged.

In my 2017, the "parasitic drain" of the trailer, with the battery switch on and nothing running, is about 6 amps per day. Back when I had an 80 amp hour lead acidcbattery, that parasitic drain would drop the voltage to around 8V in around 8 days. With a 100 amp hour battery, with 90 amp hours or so available, it would take about 15 days for the battery to use up 90 amp hours. So, with the solar on the roof, and the battery switch on, the solar only needs to replace somewhere near 6 amps a day to get the battery back to full charge. Even if the solar is only getting 3 amps a day back into the battery, and the parasitic drain is only 3 amps, it might take three months to use up 90 amp hours.

The Victron shunt is still the gold standard for battery monitoring.

Grumpy_G · October 9

pthomas745 said:

I still have not been able to figure out what these "bluetooth" apps from the battery are actually measuring, or how they measure it. They appear to cause more confusion than useful data, especially when the Victron devices and the "battery app" somehow do not agree. If they are simple voltmeters, then in every case, a Victron shunt will be more accurate.

The Victron shunt is still the gold standard for battery monitoring.

The Victron shunt *was* the gold standard in the days of lead acid batteries. It measures voltage drop across a resistor and calculates the current from it, and in turn over time the amount of energy. It has no insight into individual cells and can't disconnect the battery to protect it. It also needs manual configuration to be the most useful.

Technically speaking the apps don't measure anything, they merely display data from the BMS. The BMS contains the same shunt style of current measurement, plus temperature tracking, cell disconnect/reconnect depending on level of charge, and cell balancing. Sidenote: The typical LiFePo batteries used in RVs use passive cell balancing, meaning the higher voltage cells get bled down via a resistor and then charged up again in parallel with the lower voltage cells. This screws a bit with the capacity calculation because the bled off energy does not actually end up in the cells.

HardFault · October 9

I'd use a clamp meter to determine if there's a parasitic load or a device that is "on" that you're not aware of.

Sorry for the following impersonal AI-generated instructions, but AI did in 30 seconds what it would have taken me an hour to do. Here goes:

🔍 Parasitic-Draw Check — 2018 TAB 320 CSS

(using a DC clamp meter that reads down to 10 mA)

⚙️ Tools Needed

DC clamp meter (with 10 mA or better resolution)
(uni-t ut210e digital clamp meter $60 tests via clamp down to 1mA)
Access to battery, 12 V fuse panel, and AC breaker panel

🧰 Prep

Unplug shore power from the trailer.
Cover or disconnect your solar panel (to prevent backfeed).
Let the system rest for 2–3 minutes so any capacitors or electronics discharge.
Ensure all lights, fans, fridge, and accessories are off.
Confirm battery disconnect is ON — you’re testing the trailer’s full resting draw.

⚡ Step 1 – Baseline DC Draw at the Battery

Set the clamp meter to DC Amps (A).
Press ZERO (tare) with the jaws empty. (if your meter has a tare function. That's essentially tells the meter to set it's display to 0.0A under it's current conditions) Clamp around one cable only (preferably the negative battery cable).
Keep the wire centered in the clamp jaw.

Read the display and note the current.

Reading	Interpretation
0.00–0.02 A (0–20 mA)	Normal standby draw
0.03–0.10 A (30–100 mA)	Acceptable if LP detector or radio memory is active
> 0.10 A (100 mA +)	Parasitic draw—track it down
> 0.50 A (500 mA +)	Significant drain—battery will drop quickly

⚙️ Step 2 – Check the AC Breaker Panel

Even though the trailer is unplugged, the AC breakers can control circuits that feed converter/charger components that backfeed the 12 V system when shore power is available.

Locate your AC breaker panel (usually near the 12 V fuse panel).
Turn OFF all breakers.
Observe the DC clamp meter.
- If current drops, the converter or charger circuit may have standby leakage even when “off.”
Turn breakers ON one by one, watching for a jump in current.
- The main and converter breakers are the most likely to affect DC draw.
Leave all breakers OFF during final DC testing to isolate DC-only drains.

🔋 Step 3 – Isolate the DC Circuits

Move to the 12 V fuse panel.
Keep the clamp on the battery negative cable.
Pull one fuse at a time.
Wait 3–5 seconds after each pull for the meter to stabilize.
When the reading drops sharply, you’ve found the culprit circuit.
Reinsert the fuse and confirm the reading goes back up.

If the reading stays high with all fuses pulled:

The draw is likely before the fuse panel (e.g., solar controller, hitch wiring, or battery monitor, etc).

🔧 Step 4 – Confirm and Pinpoint

Check devices on the suspect circuit (radio, USB ports, fridge board, water pump controller, etc.).
Unplug or disconnect each one until the current drops to the normal range.
Document the result — note the amperage, circuit label, and which device caused it.

🧮 Optional Multi-Turn Trick

If the reading is too low to stabilize:

Loop the same battery cable twice or three times through the clamp.
Multiply the reading by 1 ÷ number of loops (two loops → divide reading by 2).
- Example: Clamp shows 0.18 A with two loops → true draw = 0.09 A (90 mA).

🪫 Step 5 – Wrap Up

Reinstall all fuses and reset breakers to normal.
Uncover or reconnect the solar panel.
Plug in shore power if desired.
Record your “normal resting draw” for future comparison (helps spot new issues early).

kipwill · October 9

OK, I think everyone agrees that the SeeLevel battery gauge on the wall of our 2018 TAB doesn't give accurate data, especially now that we have a lithium battery.

I left our TAB connected to shore power overnight, and have power disconnected now. Since we don't have a Victron shunt installed at this time, I used the LiTime app to check on our battery. It is a 12V 100Ah Group 24 Bluetooth battery with low-temperature charging cut-off protection.
.
With power turned on (green) the app tells me that the battery presently has 78 Ah capacity, 13.5 V voltage, is functioning normally, and our BMS is "running smoothly." I'm sorry I don't have the Victron shunt to see if that would give me a significantly different reading.

When I turn the power off (red), it reads 18.3 W power, 1.4 A current,13.5 voltage, and 78 Ah capacity. I'm thinking that indicates the battery should be good for at least a couple of days, especially if we use shore power to top off battery before we leave and have some sun as we travel or camp.

Sharon, I don't think we have an inverter.

Additional input still very welcome!

Grumpy_G · October 9

Need ... more ... data. It's somewhat puzzling that you see current with the battery switch off unless it's the solar panels charging.

Shore power disconnected, battery switch on - what does the app show for charging/discharging state and what is the amperage ?

Same for switch off - charging/discharging and amperage ?

78 Ah capacity is ballpark what can be achieved with the standard converter in the trailer. If the solar charger configured correctly for LiFePo batteries it should be able to increase that to 100 Ah, given enough time.

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