A good boat electrical system starts with the loads, then works backwards through energy storage, maximum current, charging capacity, cable size, over-current protection, monitoring, redundancy and the physical installation environment.
This guide is designed for Australian boat owners who want to understand that entire chain, then apply it to a specific vessel, load profile and cruising region.
What this guide covers
- How many amp-hours does my boat need?
- Is 200Ah enough for a weekend cruiser?
- Is 400Ah enough for Starlink and a fridge?
- Can I run a washing machine from lithium batteries?
- Can lithium run marine air conditioning?
- Should a yacht use 12V, 24V or 48V?
- What size inverter do I need?
- What BMS current rating do I need?
- How much solar should I install?
- Can my existing alternator charge lithium?
- Do I need a DC-DC charger?
- Can I keep my AGM starter battery?
- Is an IP67 battery actually waterproof?
- What happens if salt water reaches a lithium battery?
- Can I connect four batteries in parallel?
- Is one large battery better than several smaller batteries?
- What should I ask a marine electrician before an installation?
- How should I compare marine lithium batteries sold in Australia?
Start with energy, not amp-hours
A battery marked 12.8V 400Ah stores approximately:
12.8 V x 400 Ah = 5,120 Wh = 5.12 kWh
A 25.6V 200Ah bank also stores:
25.6 V x 200 Ah = 5,120 Wh = 5.12 kWh
The amp-hour number is different, but the stored energy is the same.
That is why this guide uses watt-hours and kilowatt-hours whenever systems of different voltages are compared.
Learn Ah vs Wh
Calculate your boat's daily power use
Compare 12V, 24V and 48V
A practical marine lithium system
A complete system may include:
- LiFePO4 house battery bank
- Battery Management System
- Main battery fuse or appropriately rated breaker
- Main battery isolator
- Positive and negative busbars
- Battery monitor and shunt
- Alternator charging interface
- DC-DC charger or regulated alternator system
- Solar panels
- MPPT solar controller
- Shore-power charger
- Inverter or inverter-charger
- Generator charging
- DC distribution
- AC distribution
- Alarm and monitoring system
- Temperature sensing
- Correctly sized marine cabling
- Appropriate cable protection and strain relief
- Safe battery mounting and environmental protection
The battery itself is only one component.
Typical boat energy levels
| Boat use | Indicative daily energy | Common battery range to investigate | Typical charging approach |
|---|---|---|---|
| Day sailing / fishing | 0.3-0.8 kWh/day | 100Ah at 12V | Alternator + optional 100-250W solar |
| Weekend cruiser | 0.8-1.8 kWh/day | 200-300Ah at 12V | 300-500W solar + alternator |
| Coastal cruiser | 2-4 kWh/day | 400-600Ah at 12V or 200-300Ah at 24V | 600-1,200W solar + alternator |
| Full liveaboard | 4-8 kWh/day | 8-15 kWh bank | 1,000-2,000W solar + engine/generator backup |
| High-energy liveaboard | 8-15+ kWh/day | 15-30+ kWh bank | Large solar + generator/alternator/hydro |
| Electric propulsion vessel | Highly variable | Engineering-specific | Purpose-designed high-voltage system |
These are planning ranges, not purchase recommendations.
