All guides · Batteries and charging
I choose based on the battery voltage and charging instructions first. Then, I look at how much power needs to be put back into the battery and how long you typically have shore power available.
Start with the battery data sheet
A charger for a 12 V battery and a charger for a 24 V battery are different products. Then, check the chosen charging profile against the battery manufacturer's requirements. Labels like AGM or lithium are a starting point; the specific charging voltage, permitted current, and temperature control must also match.
On an adjustable charger, the factory setting is not necessarily the right one for your boat. For LiFePO4, the BMS and any protection against charging at low temperatures must be included in the assessment.
How many amps do you need?
Look at what you need to recharge after a trip. If you have typically used 60 Ah, that is more relevant than simply choosing a charger based on the total battery capacity. At the same time, account for the refrigerator, lights, and other equipment that are switched on during charging.
Calculation example: an evening in the harbor
Assume the battery is 60 Ah short. A 20 A charger, which simultaneously supplies a constant consumption of 5 A, theoretically leaves 15 A for the battery. 60 Ah / 15 A = 4 hours.
This is a simplified minimum calculation, not a guarantee of a full charge. When the charger or battery reduces the current later in the charging process, it will take longer.
Three outputs do not mean three times the power
On the Victron Blue Smart IP22 with three outputs, the charger's total rated current is shared between the outputs. A 30 A model, therefore, provides a maximum of 30 A in total. Furthermore, the outputs are not three completely independent chargers, each with its own optional battery chemistry.
If you have, for example, a starter battery and a service battery with different charging needs, I would check the compatibility specifically. The number of batteries does not alone determine how many outputs you need; several interconnected batteries can form one bank.
Location is part of the choice
- Moisture and ventilation: Choose a charger that the manufacturer allows for the planned location.
- Noise: Check the fan and any night mode if the charger is to be placed near a berth.
- Cables: Measure the distance to the battery and have the cable and fuse selected together with the charger.
- Operation: Consider whether you want to be able to monitor the charging process in an app or on a display.
A fixed 230 V installation requires correct protection and workmanship. This guide helps with product selection; use the charger's installation manual and a qualified marine electrician for work on the shore power system.
My starting point for a quote
Send the battery model, number of battery banks, typical daily consumption, and how long you usually stay with shore power. Then I can help weigh the price, charging time, and installation requirements.
Sources and manufacturer documentation
This guide was written by SejlStrøm. Technical information was verified on September 22, 2026. Always use the documentation for the exact model and version.