The essentials in 30 seconds
- Batteries: follow the manual. Victron: lithium kept charged, or nearly full then disconnected. Mastervolt MLI Ultra without shore power: above 80%, relay in LOCK OFF, recharge recommended every 100 days.
- Lithium and cold: Victron allows charging only between +5 and +50 °C; the BMS must cut off chargers.
- Removable displays at home, updates during winter on a stable power supply.
- Speed log: plug the intake, drained before freezing; no high pressure on transducers. At relaunch, check for leaks immediately, then within 3 hours (Airmar).
- In spring, measure before sailing: about 60 Ω and at least 9 V on the NMEA 2000, VHF VSWR, autopilot tested at the dock.
Contents
This checklist covers electronics and battery storage during the lay-up; the energy refit (battery bank, charging, lithium conversion) has its own method in our energy refit winterizing checklist. General rule: the manufacturer’s manual overrides dockside habits, and it varies by brand.
Batteries: store according to the manual
A "standby" bank continues to draw power (alarms, relays, standby modes, charger feedback), reminds the Victron Lithium Smart manual. After a low-voltage BMS cutoff, approximately 1 Ah remains per 100 Ah: 10 mA is enough to damage a 200 Ah battery left discharged for more than 8 days. Before departure, read the current draw with everything off on the battery monitor (SmartShunt, BMV…): unexplained draw indicates a load to locate.
| Battery | Manufacturer's instructions | Watch points |
|---|---|---|
| Victron Lithium Smart (e.g. 12.8 V/330 Ah) | Maintained on charge, or (almost) fully charged then DC system disconnected: battery switch, fuses, or positive terminal. BMS cutoff is a last resort. | Charge only between +5 °C and +50 °C. |
| Mastervolt MLI Ultra (12/3000, 12/6000, 24/6000) | Storage for more than 3 months. With shore power: loads disconnected, floating at 13.5 V (27.0 V for 24 V). Without shore power: above 80 %, relay in LOCK OFF, MasterBus not set to "Always on", recharge above 80 % recommended every 100 days. | Below −5 °C, charging may be refused. |
| Victron AGM and Gel | Up to one year without recharge, stored cool. Victron chargers' storage mode: 13.2 to 13.5 V (12 V), weekly absorption recovery. | Self-discharge less than 2 % per month at 20 °C, doubling for every +10 °C increase. |
| Mastervolt AGM 12 V | "Keep batteries charged"; recharge as soon as open-circuit voltage drops below 12.3 V, and at least every 9 months below 20 °C. | Self-discharge approximately 3 % per month at 20 °C. |
Workshop trap: lithium, charger and cold. Keeping a lithium under charge in winter requires the charge to be cut below the minimum temperature. At Victron, it is the BMS that controls the chargers, default threshold +5 °C, because a cell charged below this suffers permanent damage. The manual also calls for at least 2 hours of absorption per month, and a possible charger "storage" mode set to floating (13.5 V for 12.8 V). Otherwise: nearly full, then disconnected.
Displays and chartplotters: remove, protect, update
Check each unit's storage range (−20 to 70 °C for Garmin VHF 115/215, for example): outside this range, Garmin excludes water damage from warranty. Moisture remains a risk: condensation can rarely form under the lens of Garmin chartplotters after large temperature swings; a hydrophobic membrane vents it when the screen heats up, and Garmin advises storing the unit warm, in the house or garage, when not in use.
- Display on bracket: at home, photograph connections, leave plugs on board protected.
- Flush-mounted display: on board, powered off, boat ventilated, cover in place (Raymarine requires this when not in use, to protect against UV). Removing it affects the mounting gasket and connectors: plan the job.
- Cleaning: powered off, damp cloth, no solvents or high-pressure wash (Raymarine).
Updates: now, not in April. An interrupted update can leave the unit non-functional, Raymarine warns, and requires reliable power and a prior backup; its full package covers Axiom displays and networked products, via Wi-Fi or microSD. On Garmin GPSMAP units, the memory card prepared with Garmin Express is inserted while the chartplotter is fully powered on and remains in place until a full restart. Also check your chart subscription expiry (marine chart comparison).
Depth sounders and through-hull fittings at the water exit
When dry, check the watertightness of through-hull fittings from both sides. For a paddlewheel transducer on a through-hull with a flap valve, such as the Airmar DST810, Airmar’s manual requires:
- no electric sander or pressure washer on the transducer, as these can weaken the structure or internal components: inform the yard;
- the sealing plug installed immediately after exiting the water (or within a week in salt water), with intact and greased O-rings, hand-tightened nut, and safety wire refitted;
- when dry, remove the plug to allow water to drain, then reinstall it; failure to do so can cause the plastic to crack due to freezing;
- clean with Scotch-Brite and mild detergent, without scratching the face, and never with solvent;
- apply water-based antifouling designed for transducers, never ketone-based, every 6 months or at the start of each season.
Lost, broken, or worn part: replace without delay; broken flap valve: replace the through-hull fitting at the next water exit. The flap valve is not a watertight seal; only the insert or plug closes the passage. When relaunching: immediate check, then no more than 3 hours without a new inspection; a small leak can accumulate a significant amount of water in 24 hours.
Mast down: sensors, antennas, connectors
With the mast lowered, B&G and Garmin recommend removing their wireless wind transducers, with different battery instructions:
- B&G WS320: remove the aerial from the mast and remove the battery for winter to prevent discharge; the pairing with the base station must be redone on the ground before reinstalling the transducer.
- Garmin gWind Wireless 2: store in a dry, light place to maintain the battery between 0 and 35 °C; stored in the dark, replace the battery at the start of the season.
At the mast foot, plug, bag, and label each unplugged connector (VHF, instruments, radar, lights); Garmin even supplies caps for unused VHF ports to prevent contact corrosion. Inspect the VHF/AIS coaxial cabling: mast foot and rear of the unit, plus antenna and head plug if the mast is down. A corroded PL259 can be repaired by recutting the cable (PL259 crimp connector for RG213/RG214); at re-masting, an SWR check validates the entire setup (VHF masthead vs. cockpit antenna).
NMEA 2000 network: corrosion and spring checks
In its troubleshooting procedures, Raymarine requires tight, clean, and corrosion-free connections; otherwise, replace them: apply this rule to the NMEA 2000 bus, starting with connectors exposed to moisture (bilges, mast foot, cockpit). For Micro-C, T-connectors and terminations are common parts (B&G Micro-C T-connector, Navico TR-120 terminations). In spring, two measurements are documented by Actisense:
- network powered off, approximately 60 Ω between NET-H and NET-L (two 120 Ω terminations in parallel); 120 Ω: one missing, 40 Ω: one too many;
- at least 9 V between NET-S and NET-C at the end of each branch, termination removed during measurement; the network must remain between 9 and 16 V.
Architecture and power supply: our guide NMEA 2000 on sailboat.
Autopilot and ram
Mechanical maintenance of the ram is detailed in our article ram maintenance. Note the season’s symptoms as soon as the boat is out of the water and plan a dockside test in spring, especially if rudder, drive or heading sensor have been affected. Monitor anything stored near the heading sensor: Raymarine cites ferrous hardware and tools, speakers, pumps, electric motors and high-current cables, and recommends relocating the heading sensor on Evolution autopilots if deviation reaches 15°.
Costly spring mistakes
Each stems from a previously mentioned instruction, forgotten or incorrectly applied:
- the lithium bank isolated by the BMS, drained by forgotten consumption;
- the charger left connected to a lithium bank in a cold boat, without BMS isolation;
- the log transducer cracked by frost, or the impeller seized due to missing transducer cap;
- the transducer cleaned with a pressure washer or painted with the hull antifouling;
- mast foot connectors left exposed, then intermittent failures;
- the update launched the day before departure, on a weak battery;
- the wireless wind sensor silent: dead battery or pairing forgotten.
Limits and pitfalls
- A single manual applies to an entire range: for any battery not listed in the table, use its manual, latest revision.
- Wintering is not repairing: an end-of-life bank or a jury-rigged network require a refit.
- Suspect through-hull fittings (crack, leak, valve): intervention ashore, not “we’ll see afloat.”
- Without a multimeter or SWR meter, the checklist remains visual.
Workshop verdict
- Ashore, without shore power: bank charged then isolated per its manual, removable displays and wireless sensors at home, log transducer plugged and drained, connectors capped.
- Afloat all winter: the automatic bilge pump remains powered, so the bank does too, via a charger set per the battery manual (table above). Log transducer plugged beyond one week without sailing, regular checks.
- Electronic work this winter: updates after installation (Garmin requires this for its through-hull transducers), then network measurements and autopilot test before relaunch; see our sailboat electronic refit method.
Outsource: the Skysat workshop in Carnac installs, configures and commissions onboard electronics and power systems (NMEA 2000 network, autopilots, lithium). For updates or recommissioning before the season, describe your system from the Our services page.
Sources
- Victron Energy: Lithium Smart manual (rev. 21); Gel and AGM datasheet.
- Mastervolt: MLI Ultra manual (10000019442/11); AGM 12 V manual (10000002887/09).
- Airmar: DST800/DST810 installation guide (17-435-01 rev. 16).
- Garmin: installation instructions for thru-hull transducers, VHF 115/215 and gWind Wireless 2; GPSMAP manual; NMEA 2000 technical reference; FAQ on chartplotter fogging.
- Raymarine: LightHouse 4 updates; Axiom 2 Pro installation guide (87443 rev. 7); Evolution setup FAQ.
- B&G: WS320 installation guide (988-12029-001, 988-12029-002).
- Actisense: NMEA 2000 network testing guide.
