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Winter Battery Storage & Maintenance

October 12, 2009 by Mark Polk · 12 Comments 

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battery 018I was recently asked a question and felt like the answer could be useful to lots of RVers, so I am using the question as the topic for this article.

Q: Hi Mark, we live in Colorado and we are preparing our RV for storage. I just had the RV winterized, but I am concerned about how or what to do to store my RV batteries. Any advice would be appreciated.

A: 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, like during storage. 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. With that said let’s look at how to properly store your RV batteries.

Before we talk about storing the batteries we need to talk about battery safety. Lead acid batteries contain sulfuric acid which is extremely corrosive and can cause severe burns or even blindness. And the hydrogen gas that batteries produce, when they’re charging, is very explosive. When you work around batteries you need to wear safety glasses and gloves, remove all jewelry and do not smoke or use any open flames.

 Caution: If you accidentally get battery acid on your skin, flush it with lots of water and if it gets in your eyes flush with low pressure water for 15 minutes and call a doctor.

 When you put the RV in long term storage it’s a good idea to remove the batteries and put them in storage too. This is quite simple to do. The first thing we want to do is visually inspect the batteries for any obvious damage. Any fluid on or around the battery may be an indication that electrolyte is leaking from the battery. A damaged or leaking battery should be replaced immediately. Whenever you remove any battery always remember to remove the negative terminal or cable first, and then the positive cable.

Battery Tip: When you remove a battery turn off the ignition switch, all electrical switches, and any battery disconnect switches before you disconnect the battery cables. Whenever you remove any battery cables label them first so you remember how they go back on the battery next spring. When you reinstall the battery do it in the reverse order. Install the positive cable first and then the negative cable.

Clean the batteries with a 50/50 mixture of baking soda and water if necessary. Now you can check the electrolyte level in each cell and add distilled water if necessary. The minimum level required, before charging a battery, is at the top of the plates. If it’s below the plates add enough distilled water to cover the plates before you charge the battery.

 Test the battery state of charge with a voltmeter or hydrometer and charge any batteries that are at or below 80% state of charge. An 80% charge is approximately 12.5 volts for a 12-volt battery and 6.25 volts for a 6-volt battery. Lead sulfation starts when a battery state of charge drops below 80%. After charging the batteries check and fill each cell to 1/8 inch below the fill well with distilled water. Overfilling cells will cause battery acid to overflow.

 Caution: Batteries should only be charged in a well ventilated area and keep any sparks and open flames away from a battery being charged. Check the electrolyte levels before and after charging batteries.

 A discharged or partially charged battery will freeze much faster than a charged battery. Store the batteries in a cool dry place but not where they could freeze. Batteries in storage will loose a percentage of current through internal leakage. It’s not uncommon for a battery to discharge up to 10% a month when it is being stored. Cold temperatures slow this natural discharge process down and warmer temperatures speed the process up. Test the stored battery state of charge every month and charge batteries that are at or below an 80% state of charge.

 Completely charge the batteries before re-installing them next spring. For optimum performance you can equalize the batteries after they are fully charged.  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. Equalizing is fine as long as there is not excessive heating or electrolyte boiling over. Some battery chargers have an equalization cycle or charge setting. After charging a battery, set the battery charger on equalizing voltage and charge it again. 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 will need to add distilled water to the cells.

Note: If you don’t feel comfortable working on or around lead acid batteries have battery maintenance done by an authorized service center. 

If you decide to leave the batteries in the RV while it is in storage remember to check the state of charge monthly and charge any batteries at or below an 80% charge. If your RV converter charger charges the battery(s) at a constant rate (around 13.5 volts) this is too high for a float charge and can deplete the electrolyte over time. In this situation plug the RV in periodically  and allow the converter charger to charge the battery(s) for 8 to 12 hours. Some RV converter multi-stage chargers and aftermarket chargers are designed to maintain a float charge on the battery without removing the batteries from the RV. Remember, for the converter charger to work the RV will need to be plugged in to electricity.

 Watch a video clip on Saving your RV Batteries 

For more in depth information on RV batteries check out our Deep Cycle Battery Care & Maintenance DVD 

Happy Camping,

Mark Polk

RV Education 101

RV University

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