Batteries by size
400Ah Lithium Boat Batteries: 12V Capacity and Runtime
These examples allow 320 Ah usable from a 400Ah battery using an 80% planning allowance. This is a reserve assumption, not a universal battery limit. Everything below is worked from 320 Ah, not from the number on the label.
On a single charge
400Ah battery runtime by appliance
Run times if that load were the only thing on the boat. Real boats run several at once, which is why the calculator sums them rather than letting you read a single row.
| Load | Draw | Run time on 320 Ah |
|---|---|---|
| VHF + AIS on standby | 0.9 A | 15 days |
| Fans | 1.2 A | 11 days |
| Cabin + nav lights | 2.0 A | 7 days |
| Instruments + chartplotter | 2.2 A | 6 days |
| Laptops, phones, tablets | 3.5 A | 4 days |
| Freezer | 4.0 A | 3 days |
| Autopilot (passage days) | 4.5 A | 3 days |
| 12 V fridge (45% duty) | 5.0 A | 3 days |
| Freshwater + shower pump | 7.0 A | 45.7 hours |
| Watermaker | 25.0 A | 12.8 hours |
Against real boats
Example overnight loads and battery bank capacity
| Hull | Daily draw | Nights on one 400 Ah | Cases for one night |
|---|---|---|---|
| 12 ft tinnie | 14 Ah | 22.9 | 1 case |
| Bowrider | 50 Ah | 6.4 | 1 case |
| Half cabin | 75 Ah | 4.3 | 1 case |
| Offshore centre console | 110 Ah | 2.9 | 1 case |
| Trailer sailer | 55 Ah | 5.8 | 1 case |
| 38 ft cruising yacht | 149 Ah | 2.1 | 1 case |
| Cruising catamaran | 260 Ah | 1.2 | 1 case |
| Houseboat | 320 Ah | 1.0 | 1 case |
| Liveaboard | 220 Ah | 1.5 | 1 case |
Daily draw is the load profile published on each hull page, quoted in 12 V amp-hours. Cases are the number of 400 Ah batteries needed to cover one night with nothing coming back in — before solar, and before the reserve you should be holding for weather.
The options
Compare listed 12V 400Ah lithium batteries
| Battery | Price band | Per usable Ah | Weight | Warranty | Bench |
|---|---|---|---|---|---|
| Revolution 12 V 400 Ah | $2,800–$3,700 | $10.16 | 46 kg | 4 yr | claimed |
Pricing is indicative and not yet independently verified. Bands are compiled from published market pricing, not from quotes we obtained. No brand has paid to appear or be ranked.
Asked most
How long will a 400 Ah lithium battery last?
A 400 Ah LiFePO4 gives about 320 Ah usable using this site’s 80% depth-of-discharge planning allowance. On a boat drawing 13 A continuously that is roughly a day. The honest answer depends entirely on your loads, which is what the calculator is for.
Is 400 Ah enough for my boat?
On its own, 400 Ah covers a night at anchor for 9 of the nine hull types we publish load profiles for, including a 12 ft tinnie. Bigger boats need it multiplied: size the bank from your own loads rather than from a capacity you have already picked.
What does a 400 Ah lithium battery cost in Australia?
Indicatively $2,800–$3,700 at the budget end and up to $2,800–$3,700 for the marine-specific brands. Those bands are compiled from published pricing and are not quotes; confirm with the retailer.