Watering & Testing Batteries

Perhaps the most routine task servicing batteries is the most important, – the watering and testing of batteries is absolutely critical to long life and problem free service. It is imperative to monitor and maintain water levels; nearly as important is routinely testing batteries, watching for signs of poor performance. One bad battery can drag down entire battery bank, if ignored long enough a few bad batteries can leave you with a next to worthless system.

The first sign of a problem is typically the batteries not holding power like they use to, they cannot handle loads for very long and they quickly shed voltage at a certain point, – typically they hold a moderate load until a certain point and then the bottom falls out rapidly. Say your 24-volt system will hold well until sundown, and then remain stable until 23.4 volts, and then the bottom will fall out within 30 minutes; this is a sign one or more batteries are bad or underperforming, dragging your good batteries down. This pattern can be subtle at first, but over time it will worsen and become very noticeable, but it is better to catch this early as the harm can become cumulative.

The general outline of general service follows, it is very basic and takes only half an hour, but it must be done religiously once a month, possibly more often if your batteries are older or weak, some failing batteries will consume more water and even feel warm (a bad sign usually).


  1. Wear goggles and long sleeves
  2. Use only distilled water
  3. Use a proper battery filling bottle
  4. Do not overfill
  5. Perform this task religiously, at least once a month, older batteries more often as needed. NEVER FORGET!

The better you do the above, proper watering and maintaining proper care (equalizing regularly, not overcharging or undercharging, keeping batteries cool) the longer the batteries will give good service. When batteries get old, start to have problems maintaining power, or consumes more water, these are signs that you need to closely monitor batteries, – test the individual batteries voltage more often and checking the specific gravity of the electrolyte in each cell.


  1. Test voltage of each battery individually (with a multimeter), look for batteries that are significantly lower voltage than the others.
  2. Use a battery tester (battery hydrometer) to check the specific gravity of the electrolyte in each cell. It will tell you the health of the cells, one bad cell means the battery is failing, often this is enough to cause poor performance of an entire battery bank. Worse, over time it can harm other batteries multiplying your problem.
  3. Do both more often if you are experiencing poor performance or the batteries are old, especially if the water consumption (in each cell) rises. It is imperative that the water level stays above the plates.

Another method I have found useful is when the batteries are charging (with a generator) to test the voltage of each battery, a weak or bad battery will take a charge faster, – if you have a couple bad batteries you will find that charging takes a shorter time interval, this is because it has a lower capacity due to its state. This is very disruptive to your charging process; your inverter will be measuring battery voltage and will cut out charging due to the voltage readings these bad batteries are producing. Meaning that a normal charging of a couple hours will kick the charging process off in perhaps 30-45 minutes and the good batteries will not be charged properly, requiring a repeat of the process. If you notice your battery voltage rising rapidly during the early stage of charging, drawing/taking less power in, then you should test your batteries to see if you have a bad battery (more likely more than one).

Recommended Books:

The 12 Volt Bible for Boats Managing 12 Volts Solar Electricity RVer’s Guide to Solar Battery Charging Basic Electricity  Living On 12 Volts With Ample Power


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