BoatHowTo · video

What this video covers

Jan Attenstedt and Nigel Calder explain that a standard multimeter provides unreliable battery health data because voltage readings fluctuate based on recent charge or discharge currents.Watch To accurately test battery capacity, a user must fully charge the battery and then apply a constant load while tracking amp-hours via a battery monitoring system.1:09 A true capacity test requires discharging a 12-volt battery down to 10.5 volts, though this process causes minor internal damage and should be performed sparingly.1:26 During this discharge, voltage drops slowly until it reaches approximately 11 volts, at which point the decline accelerates rapidly, necessitating close monitoring to prevent over-discharge.3:13 Alternatively, users can monitor for sulfation by observing if a battery charges faster than usual or delivers fewer amp-hours than its nominal rating.2:14 Comparing resting voltage against published state-of-charge charts after a partial discharge offers a rough estimate of health, though this method remains imprecise.1:55 Quality AGM or gel cell batteries should last eight to ten years under proper duty cycles.3:47

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