How to Know If a Deep Cycle Battery Is Badby Anthony Smith
Deep cycle batteries are well suited for marine, RV, solar power and similar applications. They are different from your average car battery, and they must be maintained and checked regularly to get the best performance from the battery and the system to which they are connected. Part of this maintenance is the testing of deep cycle batteries to see if they are in need of replacement.
Do a visual inspection of the battery. If there is any damage to the battery case or terminals, the battery should be replaced. Check the electrolyte level and make sure that the battery plates are covered.
Charge the battery fully before testing. Remove any surface charge to the battery by putting it to use in its application for a few minutes.
Have a copy of the manufacturer's specifications for the battery nearby, as you will need to refer to them as you test the battery.
Take a hydrometer reading of all the cells in the battery. This is as simple as squeezing the bulb and releasing it so that it sucks up some electrolyte, and then reading the specific gravity measurement. Refer to the spec sheet for the minimum acceptable reading and difference of specific gravity between cells.
Take a voltage reading with the voltmeter and compare it to the manufacturer specs for a fully charged battery.
Follow the instructions for the digital load tester, and test the battery while it is being placed under a load. This type of tester will not necessarily measure the battery capacity, but it will indicate whether or not the battery has an interior defect. A battery that fails any of the tests with these methods will need to be replaced.