Having the right tool for the job always makes the task easier. I’ve posted about battery maintenance before. To recap, the house 12-volt system on our coach is powered by four 6-volt deep-cycle batteries. In our case, they’re golf cart-type, flooded wet-cell lead-acid batteries. This means the cells have lead plates immersed in electrolyte. The electrolyte is 65% water and 35% sulfuric acid.

To produce 12 volts from a bank of 6-volt batteries, they’re connected in pairs. Two 6-volt batteries connected in series produce twelve volts. Each of our four 6-volt batteries is rated to 186 amp hours (AH). This rating is typically taken over a 20-hour period. In other words, the battery should provide a little over 9 amps for 20 hours. In reality, you never want to completely discharge a battery. There’s another factor as well – discharge rates aren’t linear. The higher the discharge rate, the less capacity the battery can provide. In our case, the batteries are rated for 100 minutes at 75 amps. If it were linear, you would expect close to 150 minutes (186/75=2.48 hours).

Our two pairs of batteries connected in series amounts to two large 12-volt batteries. The two pairs are connected to each other in parallel so the voltage remains the same, but the capacity is equal to the sum of the two battery pairs. Our 186 AH batteries are now capable of providing 372 AH.

It’s important to keep lead-acid batteries charged. Storing them in a discharged state causes sulfation of the plates which diminishes capacity and ultimately ruins the battery.

Our bank of house batteries is charged by the inverter/charger any time we are connected to shore power or are running our generator. It’s a smart charger that monitors the battery condition and temperature and adjusts the charging rates accordingly. The charging goes through three phases. First is bulk charging. This phase takes care of 80% of the charging. Constant current is applied and voltage is raised above 14 volts. The second phase is called absorption. In this phase, the voltage is constant at 14.1 to 14.8 volts and current decreases as the final 20% of the charge is completed. The last phase is called float charging. In this phase, the voltage is dropped to 13.0 to 13.8 volts and the current is reduced to less than 1% of battery capacity. This phase will maintain an unused battery in a fully charged state.

The smart charger shouldn’t allow the temperature of a flooded wet cell battery to exceed 125 degrees Fahrenheit. However, some gassing of the electrolyte is inevitable. This gassing plus normal evaporation causes the electrolyte level to drop over time. The lead plates in the cells should never be exposed to air – they should be completely immersed in electrolyte at all times. Exposure to air causes irreversible damage. The evaporation or gassing only affects the water in the electrolyte. The sulfuric acid is not diminished. Therefore, only water is needed to top up the battery.

We don’t want introduce minerals into the electrolyte, so tap water shouldn’t be used. The cells should be topped up with distilled water. Whew, all that to say our house batteries need to be checked and topped up periodically. Our chassis batteries, which are used to start the engine and power the instrument panel, are maintenance-free 12-volt batteries that don’t need to have water added.

In the past, I’ve been checking our batteries every few months by removing the caps on the cells, sticking my head into the compartment and peering down into the cells. It’s easy to see if the electrolyte level is above the plates, but it’s hard to tell how high the actual level is. The cell needs to have enough electrolyte to cover the plates with about 1/4″ to 1/2″ of liquid from the plate to the surface of the electrolyte. The electrolyte shouldn’t reach the neck of the fill well though, or acid will be forced out of the vent when the temperature rises during charging.

I used to look, make my best guess and use a turkey baster to add water to each cell. The batteries in the back of the bank were a real shot in the dark as I couldn’t see into the cells very well.

Yesterday I rode the scooter to NAPA Auto Parts and bought the right tool for the job. It’s a simple thing and something I should have done long ago. It’s a battery filler with an automatic shut-off. You fill the container with distilled water, then you push the spout into the filler well on the battery cell. The spring-loaded spout opens and allows the water to flow into the battery. When the electrolyte level reaches the spout, it automatically shuts off.

Battery filler with auto shut-off and distilled water

Using this filler is a breeze. I removed the battery caps, inserted the filler spout until the flow of water stopped, then moved on to the next cell. Job done in five minutes. I didn’t have to lean into the battery bank and peer into the cells – it automatically filled each cell to the proper level.

Couldn’t be any easier

Based on my experience over the past year, I’ll do this task every three months or so.

Yesterday I walked to the RV park office and back to purchase tickets for the big fish fry on St. Patrick’s Day. My leg is getting much better. I’ll get out and enjoy the weather with another walk today. Our forecast calls for a warming trend. We should see temperatures in the high 70s today and into the 80s over the weekend.