Enough's Enough

There is a limit to everything. And knowing when a battery has had enough, could mean the difference between a battery that lasts for years or one that has to be replaced every other season. More serious than the loss of the battery, is that the battery could become dangerous, and, unfortunately, I have seen my fair share of battery explosions. I know of a situation where the battery was so seriously over charged that it melted while out boating and took out the entire electrical system. (not one piece of electronic equipment survived the failure) So, in an attempt to keep yourself from that fate, at least learn these basics.

Note: Before performing any tests on a battery, check electrolyte level and top off with only distilled water, as needed. The likelihood of a battery explosion increases significantly as the temperature and charging rate increases and the electrolyte level decreases. Replace battery if any signs that the battery has run completely dry, cracks in battery case, and/or terminal post damage.


Warning: The information on this page should not be used for "Maintenance free", "Gel" and/or "AGM" type batteries. Also, these type batteries are not always charged properly by an old fashion battery charger.
See Tools Page about "Smart Chargers"

battery charging guide

For example: In the chart above, a completely discharged 100 amp hr deep cycle style battery would take 20 hrs at 5amps to restore it to a fully charged state. If you were to charge this battery 24 hrs and it still isn't fully charged, you can probably figure that it never will. Don't waste your electricity trying to charge it any more. Especially note the short charging times necessary to restore a dead battery as your charger input increases. So never exceed this rate chart because this is when the battery starts to become dangerous.

To avoid damage, charging rate must be reduced or temporarily halted, if:

1. Electrolyte temperature exceeds 125o F (52o C).
2. Violent gassing or spewing of electrolyte occurs.

Battery is fully charged when, over a two hour period at a low charging rate in amperes, all cells are gassing freely and no change in specific gravity occurs. For the most satisfactory charging, the lower charging rates in amperes are recommended.

Full charge specific gravity is 1.260-1.280, corrected for temperature with electrolyte level at split ring.

Continuous charging with a trickle charger weakens a battery. In situations where a battery charger has to be "on line" all the time, check water level bi-weekly, add distilled water only, make sure that the charger has a cycling feature that completely shuts off all charging to the battery when charging isn't needed. Replace the charger with a newer computer controlled charger that does. Most marine automatic chargers do not have this feature as a general rule. 

For additional information about AGM, Gel, and other useful battery tips go to this web site.

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