---

Your battery monitor shows 12.1 volts.
Does that mean you’re fine?

Most guests think “anything above 12 volts = fully charged”.
But that’s not how batteries work — especially not under load.

Here’s what voltage really tells you — and when to worry.

---

⚠️ Voltage Drops Under Load

Even a full battery will show lower voltage when you’re using it:

• Water pumps
• Fridge compressor
• Anchor winch
• Inverter (for AC power)

That’s normal. The key is to watch how fast it drops — and how low it gets when devices are running.

---

🔋 Approximate Battery State by Voltage

Voltage	Capacity (no load)	Action

12.8 V

100% (fully charged)

All good

12.5 V

~80%

Still safe

12.3 V

~60%

Start monitoring usage

12.2 V

~50%

Critical – Stop unnecessary loads

12.0 V

~40%

Already damaging AGM battery

< 11.9 V

< 30%

Unsafe – Battery is degrading

These numbers vary with temperature and battery type – but the trend is always the same.

---

🧠 LiFePO₄ Batteries Behave Differently

Some of our yachts have LiFePO₄ (lithium) batteries.
They keep a flat voltage (e.g. 13.1–13.0 V) for most of their capacity, then drop suddenly.

That means:

• You can be at 20% and still see “13.0 V”
• Always use the percentage indicator, not just voltage

---

✅ How to Monitor Battery Health Onboard

• Check Simarine or Victron display (on most yachts)
• Look for state of charge %, not just volts
• Turn off inverter when not in use
• Don’t let kids charge all devices all day long
• Ask your skipper if in doubt — before it’s too late

---

🎯

Voltage ≠ battery level.
Pay attention to the state of charge — and never assume “12 volts is plenty”.

“The lights go off when the guests ignore the numbers.”