Battery Monitoring and State of Charge Accuracy
Why lithium voltage is a poor everyday fuel gauge, how a shunt-based monitor estimates state of charge, and what to check when the reading drifts.
Lithium voltage remains relatively flat through much of the discharge curve, so voltage alone is a poor everyday fuel gauge. A properly configured shunt can estimate state of charge by measuring current in and out of the bank.
Key design checks
- Install the shunt so all house current passes through it.
- Synchronise only when the battery is genuinely full under the chosen settings.
- Check current calibration and zero-current offset.
- Treat BMS app data and shunt data as complementary, not interchangeable.
Before you commit: run through the full list on questions to ask a marine lithium installer and the installation checklist.
Apply this guidance to your boat
Use this page as one input to a vessel-specific plan. Record the actual equipment, cable runs, charging sources and operating pattern aboard before choosing hardware or changing the installation.
- Measure the real load and its operating time instead of relying on a label or a generic boat profile.
- Check every proposed current against the battery, BMS, protection, cable and connection limits.
- Confirm the result against current manufacturer instructions and the rules that apply to your vessel.
Related pages
Marine Lithium Battery Installation GuideUnderstand the full installation process for a LiFePO4 boat battery bank, including design, BMS, charging, fuses, cabling, monitoring and commissioning.How to Compare Marine Lithium Battery Installation QuotesCompare yacht lithium installation quotes by battery kWh, BMS current, solar, inverter, alternator work, protection and documentation.Red Flags in a Marine Lithium Installation QuoteThe warning signs in a marine lithium installation quote, from missing charging detail to protection and BMS integration that nobody has costed.How to Size BMS Current for a BoatWhy BMS current matters more than capacity, how to size it from your largest simultaneous load, and continuous vs peak.How to Choose a Marine Inverter SizeHow to choose a marine inverter from the appliances that genuinely run together, and why a larger inverter costs you idle draw and heavier DC infrastructure.How Much Battery Reserve Should a Cruising Yacht Keep?How much energy a cruising yacht should hold in reserve for navigation, communications, pumps and engine starting before comfort loads are switched off.