The house batteries on a cruising sailboat are a big deal. They are what keep all of your essentials and gadgets running when you leave the pier. Now, if you own a small sail boat you might not have to worry about this too much, but more and more boats are carrying more and more amp hours. So, if you have (in semi-order of priority and extravagance) navigation lights, VHF, electronic navigation, auto-pilot, reefer (ice-box ~ahem~), instruments, lights, SSB, Sat Phone and an inverter for microwave, blender, TV/DVD, air conditioning, washer/dryer, etc., you might find it worthwhile to give your batteries a check up this weekend (if you have not looked at them in awhile).
1. First off, a visual inspection. Cleanliness is essential. Also, make sure there are no signs of bulging or leakage which could be indicative of a damaged cell. Make sure there is no dirt or water on the batteries and then look for corrosion at the connections or even acid. Any of these things can draw stray current from you batteries and drain them down over time. If you do notice any corrosion at the connections: disconnect the battery, clean the terminals and studs, then replace. A water and baking soda mix makes a good cleaning agent as it neutralizes any acid (make sure nothing gets into the battery itself if it has caps). When finished, a good idea is to cover these now freshly cleaned connections with some type of rust preventative (petroleum jelly, grease, Corrosion-X <-- love that stuff) to keep the connections clean. If you have a maintenance free battery (AGM, Gel Cell or the like) then you are pretty much done unless you are having issues and cleaning up the terminals did not correct it. If you have wet-cell batteries read on...
2. If you have wet-cell/flooded batteries, which are still the standard, quite common, economical and tough, you will also need to check the status of your electrolyte (recommended monthly or twice a month on new batteries until you know their needs). Open up the caps and verify the level of your electrolyte. Regardless of the batteries' charge condition the lead plates should never be visible. If your battery has been sitting on the charger all week the electrolyte will be close to its highest (because of a full charge) so if it is low you will need to add distilled water. Distilled water is recommended over tap as it is free of contaminants and minerals which can speed sulfation. The water should be close to the top of the fill tube but not touching in order to allow for expansion - see your battery's manufactures literature for exact recommended level. Trojan Batteries walks you through this process in detail here.
3. Also for wet-cell batteries, it is a good idea to regularly test the specific gravity of your electrolyte with a hydrometer (before you add any distilled water), as it can be a good indicator of potential issues. If you did not know, the electrolyte in the battery is sulfuric acid which is denser than water. As the battery discharges, the acid weakens and becomes less dense so measuring specific gravity can tell you the state of charge of you batteries. Again, Trojan Batteries spells out this testing process and provides you with a chart to compare your measurements against here. Trojan also discusses another test you can do, an open circuit voltage test. But, that starts to go past your simple weekend checkup and moves more into a maintenance day. Remember, if you have cells arranged in parallel or series the specific gravity of each should be measured and they should be close to one another. If they are not, it could indicate an issue with cell or perhaps a requirement for an equalization charge. Reconditioning batteries is a whole different discussion.
Take the time to look at your batteries this weekend if you have not seen them in awhile. Always make sure the electrolyte is topped off on wet-cell batteries. And, always keep the connections clean. Batteries will last a very long time if they are taken care of, and, given the cost of the latest set I just ordered, they are worth the effort.
Enjoy your boating this weekend and sail safe!
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