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Monday, September 2, 2013

Maintenance Free Batteries


How do I know if I have maintenance-free batteries in my motorhome or if I have to periodically check the water levels? Kirk P., (St. Louis, MO)

Kirk, I'm guessing you're referring to the automotive start battery in your motorhome. Those so-called maintenance-free batteries will have non-removable cell caps or no caps at all. Personally, I believe the moniker, "maintenance free," is really a misnomer in that even if a battery has no access to measure the specific gravity of each cell using a hydrometer, still the battery and its terminals must be kept clean and free from oxidation and corrosion. In other words, there is still maintenance to be performed if you want to get optimum performance out of those batteries. 

Rather than specific gravity readings, voltage measurements can suffice for checking the state of charge of batteries without access to each cell; (I’ve included a chart below).

Open Circuit Voltage vs. State-of-Charge for 12-volt Batteries of Various Types

                                        Battery Electrolyte Type
State of Charge       Flooded            AGM             Gel
100%                           12.6                 12.9             12.8
75%                             12.4                 12.7             12.6
50%                             12.2                 12.4             12.3
25%                             12.0                 12.0             12.0
0%                               11.8                 11.8             11.8

But if you do not see removable caps on the top of the batteries, chances are they are probably considered the maintenance-free type. Keep in mind, some batteries by certain makers may have only two caps that cover three cells each; they may not have six individual cell caps. Hope this helps!

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