Guide
RV, van and boat battery sizing: worked examples.
Three calculated examples—weekend van, full-time RV and sailboat—with every input shown so you can swap in your own.
Short answer: a weekend van with modest loads often lands around 240 Ah at 12V; a full-time RV running an inverter all day can need close to 800 Ah at 12V—or about 400 Ah at 24V. The examples below show every input so you can swap in your own numbers.
These are example inputs, not recommendations. Measure your own loads where possible. Planning assumptions throughout: 80% usable depth of discharge, 90% available capacity, 90% inverter efficiency (85% during surge), LiFePO4 bank.
Example 1 — Weekend van, 12V
| Input | Value |
|---|---|
| AC appliances (laptop, small kitchen use) | 400 Wh/day |
| Direct DC (fridge, lights, fan, pump) | 600 Wh/day |
| Inverter overhead | 8 W for 6 h/day |
| Reserve without charging | 2 days |
| Inverter load / surge; DC current | 600 W / 900 W; 8 A |
Result: 1,092 Wh/day at the battery, 2,185 Wh for two days, 3,035 Wh nameplate → 238 Ah at 12.8 V. Estimated current: 68.2 A continuous, 103.3 A surge.
Example 2 — Full-time RV, 12V vs 24V
| Input | Value |
|---|---|
| AC appliances (induction cooking, coffee, TV, laptops) | 2,200 Wh/day |
| Direct DC (compressor fridge, lights, water pump, furnace fan) | 900 Wh/day |
| Inverter overhead | 12 W, 24 h/day |
| Reserve without charging | 2 days |
| Inverter load / surge | 1500 W / 2500 W |
Result: 3,632 Wh/day, 7,265 Wh reserve, 10,090 Wh nameplate → 789 Ah at 12.8 V (159.9 A continuous, 273.7 A surge with 10 A of DC load) or 395 Ah at 25.6 V (79.9 A continuous, 136.8 A surge with 5 A of DC load). The energy is identical; the 24V system carries half the current through every cable, fuse and connection.
The always-on inverter overhead alone is 288 Wh/day here. Switching the inverter off overnight is a free saving.
Example 3 — Sailboat, 12V, mostly DC
| Input | Value |
|---|---|
| AC appliances | 300 Wh/day |
| Direct DC (fridge, instruments, autopilot, lights) | 1,400 Wh/day |
| Inverter overhead | 6 W for 4 h/day |
| Reserve without charging | 1.5 days |
| Inverter load / surge; DC current | 500 W / 800 W; 15 A |
Result: 1,757 Wh/day, 2,636 Wh reserve, 3,661 Wh nameplate → 287 Ah at 12.8 V; 65.1 A continuous, 99.6 A surge. Marine installations have their own standards (for example ABYC E-11 and E-13); see the Safety checklist.
For comparison — Off-grid cabin, 48V
3,500 Wh/day of AC loads, 10 W overhead all day, two days of reserve at 51.2 V → 225 Ah. The full working is in the battery bank sizing guide.
Turn your example into a plan
- Measure a week of real use with a battery monitor or plug-in meter.
- Enter it in the calculator (the appliance worksheet helps for AC loads) and print the planning report.
- Take the report to a qualified installer for conductor, protection and charging design.
Hardware to compare
Sponsored links. As an Amazon Associate BatteryCaliber earns from qualifying purchases. These open Amazon search results for each category—they are not tested, certified or endorsed products. Check every item’s manufacturer datasheet against your installer’s specification. Affiliate disclosure
12V-class LiFePO4 batteries
Check continuous and surge discharge ratings, low-temperature charge protection and permitted series/parallel use—not just Ah.
Browse on AmazonInverter-chargers by DC input voltage
Search by your battery’s voltage class. A voltage keyword in a listing is not proof of compatibility: match the DC input range, continuous and surge ratings (W and VA, with duration) and the battery charge profile.
Battery monitors & shunts
A shunt-based monitor measures what the calculator only estimates. Check the shunt current rating and voltage range.
Browse on AmazonBattery disconnect switches
Check DC voltage and continuous/intermittent current ratings, and where the switch must be accessible.
Browse on Amazon