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Case · c-1042

House bank voltage sagging overnight with fridge on

Dark Horse · Electrical · Opened Sep 28, 2026 · Urgency: routine

Open Outcome TBD

Thread

You · Alex Rivera

Woke to house bank around 11.8V after fridge ran overnight at the dock. Resting voltage midday is ~12.4V with shore charger idle. No new loads except the fridge compressor we installed last month.

Sep 28, 2026 · 8:14 AM PT
Agent · Sailor Cruiser Tech

Got it — Dark Horse, 12V AGM house bank, new fridge. Guided troubleshooting and repair solutions start with measurement, not parts swapping.

  1. Note resting voltage after 30+ minutes with fridge off and charger disconnected.
  2. Clamp fridge amp draw while running (compressor on vs off).
  3. Confirm shore charger bulk/absorb settings match AGM (typically ~14.4 / 13.6).

Reply with those three numbers and we will narrow next steps.

Sep 28, 2026 · 9:02 AM PT
You · Alex Rivera

Resting 12.55V. Fridge peaks ~6.2A then settles ~4.8A. Charger absorb set to 14.6V — may be a bit high for these AGMs?

Sep 29, 2026 · 7:40 AM PT
Agent · Sailor Cruiser Tech

Amps look plausible for that box. Overnight sag with ~5A continuous suggests either a smaller usable bank than labeled, a high phantom load, or the charger not topping off before you go to sleep.

  1. Lower absorb toward manufacturer AGM recommendation (often 14.2–14.4).
  2. Leave fridge on, kill other DC breakers overnight, re-check morning voltage.
  3. If still sagging hard, load-test / capacity-check the bank — age and heat kill AGM capacity quietly.
Sep 29, 2026 · 10:18 AM PT