Specifications

15
The charging of the battery should transition seamlessly from the constant-current
charge stage to the topping charge stage. This stage will complete the remaining 30%
of the charging that is needed and can last between seven and ten hours. The current
applied to the battery begins to drop as the battery begins to saturate, and the battery is
considered fully charged when the current reaches a level that is 3% of the rated
current.
The final stage for charging a lead acid battery is known as the float charge stage.
During this time, a very low current is applied to the battery to prevent self-discharge of
the battery due to leakage. A battery that has very high leakage may never reach its
saturation point. Because of this, a timer will need to be used while charging the battery
to cut off the charge after a specified threshold so as to not accidently overcharge the
battery. If overcharging were to occur beyond a voltage that the battery was able to
handle then the excess energy inside the battery would be converted into heat, causing
gassing within the battery. It is recommended that if the battery does not reach its float
charge stage after 48 hours of being in the topping charge stage that the battery be
taken off of the charge. These three stages are illustrated in the picture below.
Figure 7 – Lead Acid Battery Charging Stages
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