Mod #72: Battery Watering System

Mod #72: Battery Watering System

Submitted on: 02/20/09

     Category: electrical
Mod Rating: 12345

(33 ratings)

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Mod Description:

How often do you just sit and ponder the level of water in your RV batteries? If you are like the average RVer, you probably don’t give it much thought. The majority of flooded lead acid battery failures are caused by under or improper watering. RVs are particularly hard on batteries, constantly discharging and charging them on a frequent basis, causing them to lose water over time. And if your RV has a cheap or poorly behaving charger, your batteries can suffer an untimely death due to the charger boiling the batteries dry. One way to prevent this from happening and to ensure the long term health of your batteries is to mod your RV with a battery watering system.

Mod Difficulty:

A battery watering system provides your batteries with just the right amount of water, never over or under filling them. It works through an arrangement of hoses and valves that replace the standard battery caps. A simple squeeze bulb hand pump provides the water supply via a quick disconnect to the water supply hose. Several batteries can be safely and simultaneously filled from a remote position without ever having to touch a battery or remove a cap. And automatic control valves ensure each cell is closed when the precise water level is reached.

Installation of the battery watering system is very easy. Here are the basic steps to follow for the Pro-Fill system:

  • The Pro-Fill valves are preinstalled on manifolds that will fit batteries with a standard spacing of 2 11/16″. If your battery has a nonstandard spacing you will need to replace the manifolds with the included swivel T’s. To remove the valves, carefully rotate and twist as shown. Attach swivel T’s to valves by carefully pushing while rotating each swivel until it snaps in place.
  • Remove the existing valve caps from your batteries, then install the manifolds, turning each valve 1/4 turn to lock them into place.
  • Link the manifolds and valves together with the Pro-Fill tubing. Now cut the desired length of tubing from the open end of the included 5′ section.
  • Attach fill line to an open barb. If you are installing on more than two batteries, try to locate the fill line towards the middle of the system.
  • Cover any remaining barbs with red end caps and installation is complete.

Pretty simple, eh? Other battery watering systems, like the AquaPro, install in much the same way. To operate:

  • Insert the squeeze bulb filler assembly into a jug of distilled water. Prime bulb by squeezing until it is filled with water.
  • Remove the dust cap from the water supply line and connect it to the squeeze bulb filler assembly by snapping the quick couplers together.
  • Squeeze the bulb with firm pressure to begin pumping water into the battery cells. When the bulb becomes firm, all cells are full.
  • Immediately disconnect the squeeze bulb filler assembly from the water supply line and replace the dust cap.
  • Any water remaining in the squeeze bulb filler assembly may be pumped back into the distilled water jug. One end of the squeeze bulb filler assembly may be inserted into the other to keep the line clean and to provide a convenient way to hang the filler in a safe place between uses.

This mod detailed a basic watering system that will help most RVers with there battery maintenance woes. There are other solutions as well, such as an automated watering system that electronically determines when batteries need water. These systems are typically used with solar installations having large battery banks, but may serve you well if your RV has a monster battery bank.

TipWater after charging. Water must always be added after fully charging the battery. If your battery charger has an equalize function it is best to add water after equalizing the battery. Prior to charging, there must be sufficient water to cover the plates. If the battery has been discharged (partially or fully), the water level should still be above the plates.
TipElectrolyte levels drop during discharge and rise during charge. In addition, charging generates heat, fluid expansion and explosive gases. Watering a battery before charge (or with a low charge level) can lead to boil over resulting in potential damage of the watering system, battery and vehicle.

ModMyRV recommends these parts for this mod:
Aqua Pro’s Single Point Battery Watering System
Pro-Fill RV Edition

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15 Comments For This Mod

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  1. cccale

    my batteries slide in a compartment underneath the entry step. There isn’t a lot of room above the batteries. do you know if this mod will add additional height to the battery? Also, do you know anyone who sells the auqapro? I don’t see any retailers on their site.

  2. ModMyRV

    I’m not too sure on the AquaPro, but the ProFill adds about 1 1/2″ above the battery top. The standard cap is about 1/2″ in height so you will add about 1″.

    If you go here:

    and click on the “Distributors and Agents” link, then select “USA”, you will get a list of states where there are distributors.

  3. Bob Vaughn

    I know you are supposed to use distilled water so what is the difference to purified water??

  4. ModMyRV

    Distilled water has pretty much everything removed from it, including all minerals. It’s used primarily where mineral buildup can pose a problem like a pump or in this case, a flooded lead acid battery. Purified water is generally free from pathogens, organic and inorganic chemicals, and heavy metals. But most minerals are left behind because they tend to improve taste.

    I’m no water filtration expert but that’s a summary of what I’ve learned through researching this subject. Just know one thing: always use distilled water for flooded lead acid batteries. It will prolong their life considerably!

  5. jmt

    Why would I use 2 or 4 or 6 batteries? More than 6? Maybe just buy a generator no?

  6. ModMyRV

    Sure, you could buy and use a generator. The advantage of the extra batteries is to use AC appliances with an inverter, which produces no noise. For almost everything with the exception of your air conditioner, you can run off of batteries and an inverter. I have 6 batteries in my TT: 4 6-volt for 1 bank and 2 12-volt for the backup bank. I can go a 3 day weekend using the microwave, TV, blow dryer (I know I know, it’s the DW), etc., and still have some juice left. Sure beats hauling the generator around.

  7. cccale

    Jeez 6 batteries? where do you have those located? We haven’t been to a campsite yet with hookups (usually national/state parks) That capacity would be great. Do you have any issues with adding that much weight to your TT?

  8. ModMyRV

    The TT had the 2 12-volt batteries mounted on the tongue when I bought it. When I added the 4 6-volt batteries, I built a vented enclosure underneath the bed. This added about 300 lbs. to the front third of the TT, which is about 250 lbs. on the tongue. The battery box is the one in Mod #1 with the gray and red battery case colors and the inverter hanging off the back of the enclosure.

    I have a nice size storage area under a rear bunk bed where I offset some of the additional tongue weight with grilling stuff, chairs, etc. So my tongue weight is a reasonable 875 lbs. So far, I have had zero issues with the additional weight. I have plenty of CCC so I’m not exceeding any weights even fully loaded and ready to go.

  9. Bob Vaughn

    At what point would you have to replace the water with battery acid….It seems to me that after a while the battery acid would have to be renewed?

  10. ModMyRV

    The only time you should add acid to your batteries is if the batteries are brand new and are dry charged, i.e., no acid in them when purchased, or if somehow your batteries are totally empty of electrolyte (water/acid mix), i.e., if they tipped over and drained.

    When charging your batteries, hydrogen gas is emitted, along with a negligible amount of other gases. The acid in the battery is not lost. It’s the water component of the electrolyte that is lost, increasing the concentration of the acid in the battery. Replenishing the battery with water brings the PH back in to balance so the chemical reaction necessary to make electricity can occur.

  11. Bob Vaughn

    Thanks for the explanation about battery acid…..I had purchased some acid good thing I did not add some to my batteries…..Of all the components of the RV lifestyle the batteries are the most annoying……

  12. Bob Vaughn

    Would replacing wet batterys with sealed lead acid batteries like Optima batteries mean you could plug in your camper and forget about worrying about batteries going dry. It is too easy to not check them on a regular basis and they can go dry in as little as a month…

  13. ModMyRV

    Sealed lead acid batteries (SLA) are a good alternative for reducing battery maintenance. But there are a few things to consider.

    SLA batteries require a different charging voltage. Your current RV charger is likely not suited for SLAs. If you have a smart charger that has an SLA charging mode, then you will be good to go.

    Optima batteries, while a good battery, have much lower capacity in terms of amp hours of power when compared to the same size flooded lead acid (FLA) battery, and they are much more expensive. Keep this in mind when sizing your battery bank. Typically, it will take 3 12-volt Optimas to retain the same capacity as 2 group 24 FLA batteries.

  14. Pinebarren

    I have used battery watering systems on industrial forklift batteries. They are not foolproof! On the type I used, if the injector went bad you would not know it, it just would not water that cell. I would have to go back and check to make sure that all cells were watered, for that I could save the money and water while checking. I’d steer clear.

    Just my $.02!

  15. glistok

    The tubing is subject to mold growth and makes the system useless.

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