Water pump causes led lights to flicker when on Battery

Today I checked battery connections, water pump connections and connections at the converter power supply. All seemed fine.

The trailer is a 2017 and has two new batteries. I installed a battery monitor inside the trailer wired directly to the the batteries.

When on battery and running cabin led's and the water pump the voltage drops about .08volts on the monitor. The lights only flicker when on battery they don't flicker when plugged into 110.

Same thing happened to us last year. I tightened the wing nuts on the battery terminals. That worked for a few days then happened again. Did this a couple times and the last time it didn't help.
Two batteries bad. Swapped out both for 2 new Group 27 deep cycle and everything was fine, no dimming of lights , pump running fine , and the wingnuts stayed tight on the new batteries for the remaining 2 months of the trip. Didn't have to tighten them again.
Check the battery connections, if that doesn't help, pull the battery out, take it to Auto Zone or O'Reilly's or a battery shop and have the battery load tested. It is a free service, unless you have to buy new batteries.

Is the water pump running at speed when this happens or does it surge and cut in and out? Depending on how many faucets are open the Pump surging is normal. Your problem is normal for some RV's depending on the water Pump and how it operates. The Water Pump pulls significant amps and can cause voltage fluctuation problems. Regardless of how many batteries you have. When on Shore Power, the Power Converter keeps the DC voltage pretty static at 12.9 to 13.1 with no voltage variations. Doug

Since this is a new trailer I assume the LED lights are factory installed. Have you checked the battery voltage at the batteries first and then at the power panel with and without the pump running? Not sure how you are verifying that the batteries are charged and how much the voltage is dropping when the pump is running. You have a long trailer so the wiring could be having larger voltage drops. Is the pump on the same circuit (fuse) as the lights?

As others have commented,if the lights do not have drivers then small voltage variations can caused light intensity to change as the pump cycles. The water pump and furnace blower are the two highest current accessories unless you are running an inverter.

Three thoughts
1: Low/week/too small/bad battery
2: Bad conneciton.. Suspects 1 and 2 are the battery terminals and the chassis end of the negative cable
3: Wires way too small because the proper size costs more.

And that about covers it.

Cheap (poorly designed) LED lights that are operating without drivers. LED are VERY sensitive to changes in voltage, even going from 13.6 to 13.4 is enough to notice.

In my opinion, all automotive (and RV) LED fixtures should have a local driver to normalize the supply voltage and eliminate output fluctuation.


Sure it could be a loose connection, that's an easier thing to fix.

Even though it's a new battery it may be faulty I would have a check.

Could be loose wires or corroded connections. Or, it could be perfectly normal. It all depends on how sever the flicker is. The pump uses a lot of power compared to the LED lights. It will cause the voltage to sag when it runs. This would normally cause the lights to dim a bit.