RV Q&A by Mark Polk~ December 2008

*NOTE: At Mark's discretion, material might be edited to suit a wide audience. Due to the large volume of material and correspondence we receive, individual replies might not be possible, nor can we acknowledge receipt of submitted material. Selected questions will be answered in future issues of our RV Education 101 newsletter and on our site. Thank-you for your understanding.

Q. Mark I have had some problems with the auxiliary batteries in my motorhome and when I began researching batteries the term equalizing kept coming up, but there was no explanation as to what it means. Can you explain it to me in layman's terms?

Mark Says: I'll try my best. Battery Equalizing is a controlled overcharge on a flooded lead acid battery after it has been fully charged. Equalizing reverses the buildup of negative chemical effects like stratification, a condition where the water and acid separate and the acid concentration is greater at the bottom of the battery than at the top. Equalizing also helps remove some of the sulfate build up on the battery plates (the stuff that kills lead acid batteries). Equalizing is fine as long as there is not excessive heating or electrolyte (battery acid)boiling over. Some battery chargers have an equalization cycle or charge setting on them. In this case after you charge a battery, you set the battery charger on equalizing voltage and charge it again. In an equalization cycle, the battery voltage can rise to approximately 16 volts and be kept there for as long as eight hours. You need to test the specific gravity every hour during equalizing. Equalization is complete when the specific gravity readings no longer rise during the gassing or bubbling stage. Keep in mind if equalizing a battery is done correctly the electrolyte should not boil over but it will create a good bit of bubbling, and when the cycle is finished you might need to add distilled water to the cells.

Q. I check the water levels in my RV battery frequently, but it seems like when I leave our RV plugged into shore power for any time at all the water levels in the cells gets low in a short period of time. Any ideas as to why this happens would be appreciated.

Mark Says: Many RV converter chargers have a fixed output voltage of about 13.5 volts. What this means is when the RV is plugged into shore power and the auxiliary battery is fully charged this is too much voltage for a float charge. Over time this can deplete the electrolyte in the battery. You need a three stage charger that can provide a bulk charge to quickly restore the battery back to 90% of a full charge, then an absorption charge for the remaining 10% and finally a float charge which is at a lower voltage level to maintain the charge. There are RV converter chargers on the market that will do this, but with your current converter charger you will need to continue checking the water levels in your battery on a regular basis, especially while plugged into shore power.

Q. I have replaced 2 sets of batteries in my motorhome in less than 4 years. This doesn't seem normal to me, but I don't know what the cause of this problem is. Can you help?

Mark Says: The two most common causes for RV battery failure are undercharging and overcharging. Undercharging is a result of batteries being repeatedly discharged and not fully recharged between cycles. If a battery is not recharged the sulfate material that attaches to the discharged portions of the plates begins to harden into crystals. Over time this sulfate cannot be converted back into active plate material and the battery is ruined. This also occurs when a battery remains discharged for an extended period of time. Sulfation is the number one cause of battery failure. The second leading cause of battery failure is overcharging. Overcharging batteries results in severe water loss and plate corrosion.

The best way to prevent these problems from happening is to make sure the batteries are fully charged (in a timely manner) after using them and by checking the electrolyte level (water level) on a regular basis. You should check and adjust the water level monthly and if you leave your RV plugged in with the batteries being charged by the converter battery charger check it bi-monthly.