Electrics
Why do my boat batteries keep going flat?
Either something is drawing power you haven't accounted for, or the batteries are no longer holding charge. Measure resting voltage after 12 hours off charge, then measure the current draw with everything switched off. Batteries over about five years old are frequently the answer.
Standing draws add up quietly: bilge pump float switches, alarms, chartplotter memory, inverters left in standby and stereo head units. A clamp meter on the main negative with everything switched off shows you in seconds whether you have a parasitic load or a tired bank.
The other common cause is charging rather than consumption — an alternator that is not reaching its regulated voltage, a failed split-charge relay, or a shore charger that has quietly stopped. A marine electrician can test all three in one visit; guessing usually means buying batteries that were not the problem.
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