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That is normal for 10A+ models. If the fan is silent , internal overheating has occurred. Power cycle immediately.

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Standard manuals list 27 warnings about sparks, hydrogen gas, and acid burns. A better manual : performax+battery+charger+and+maintainer+manual+better

Performax™ 1.25-Amp Battery Charger and Maintainer at Menards® Performax™ 2-Amp Battery Charger and Maintainer - Menards That is normal for 10A+ models