How many Ah do I need for a weekend cruise?

Typical coastal cruise: 80-150 Ah daily @ 12V (fridge, lights, nav, instruments, water pump). For a 2-day weekend with LiFePO4 at 80% DoD, that's 200-375 Ah total. Double it if you run an inverter for coffee/microwave.

Is LiFePO4 worth the price premium over AGM?

For any install with heavy daily cycling (liveaboard, full-time RV, off-grid cabin), yes — LiFePO4 delivers 3-5× the cycle life at 80% DoD vs. AGM at 50% DoD. Payback in 3-5 years. For weekend-only boats cycling 20 times a year, AGM still makes economic sense.

What size battery for a 3000W inverter?

Minimum 300 Ah LiFePO4 @ 12V to support continuous 3kW without voltage sag. 600 Ah recommended if running AC or induction cooking. 24V or 48V systems need less amp-hour capacity at the same kWh.

Battery Sizing Calculator

Size a 12V, 24V, or 48V battery bank for a boat, RV, van, or off-grid cabin. Respects depth-of-discharge by chemistry and your chosen days of autonomy.

Your inputs

Daily consumption (Ah)If you have Wh instead, divide by system voltage.System voltageBattery chemistryMax depth of discharge: 80% · cycle life: 3000 cyclesDays of autonomyHow many days your bank should run the load without any solar/engine charging.

Recommendation

Recommended bank

300 Ah

Battery config

1 × 300Ah battery

Usable capacity

240 Ah

Estimated weight

36 kg / 79 lb

Cost range (CAD)

$1,320–$2,145

Days of autonomy

Your daily consumption is 120Ah. With 2 days of autonomy, you need 240Ah of usable capacity. LiFePO4 (Lithium Iron Phosphate) batteries should only be discharged to 80% depth of discharge, so you need 300Ah of total capacity. We recommend a 300Ah bank (1 × 300Ah battery), giving you 240Ah of usable capacity — enough for 2 days without any charging.

Cost range reflects a 2026-05 retail spot-check (Battle Born, Renogy, Trojan, VMAX, UPG) converted at FX 1.35 USD/CAD. Street prices vary widely by SKU and channel — confirm against your vendor of choice before purchasing.

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How the sizing works

Usable capacity, not nameplate capacity, is what runs your loads. A 200 Ah LiFePO4 bank safely delivers about 160 Ah because lithium is comfortable down to 80% depth of discharge. A 200 Ah AGM bank only gives about 100 Ah of usable energy — same sticker, half the practical capacity.

PowerLab multiplies your daily Ah draw by your days of autonomy, then divides by the chemistry’s safe max DoD, and rounds up to the next common bank size. The result is the minimum nameplate capacity that can actually run your loads for the window you chose.

Rough DoD and cycle-life rules

LiFePO4: 80% DoD, ~3,000 cycles, 10+ years typical
AGM: 50% DoD, ~500 cycles, 3–5 years typical
Gel: 50% DoD, ~700 cycles, 4–6 years typical
Flooded lead-acid: 50% DoD, ~400 cycles, 2–4 years typical

Want the full system — loads, charge sources, wire sizing, and a PDF report? Start a free PowerLab design.

Code references

The Battery Sizing math above sits inside a regulatory framework. Inspectors and underwriters look at the citations below — your installation has to satisfy them, not just produce a number that looks reasonable.

ABYC E-10 (2018, R2024) §10.7 + §10.10
Lithium-ion battery installations on a boat must include a battery management system (BMS) that disconnects on cell over/under-voltage, cell over-temperature, and over-current. The battery compartment must be vented or the chemistry rated for sealed installation per the manufacturer.
Why it matters: For marine LFP banks sized by this calculator, the BMS and ventilation requirement gates the install — pick a battery whose datasheet explicitly meets E-10's disconnect criteria, not just one with a generic "BMS included" badge.
ABYC E-11 §11.10.1.3.1 (2018) / Supplement 65 (2025)
Battery positive cables require an overcurrent device within 7 inches of the battery positive terminal (or up to 40 inches if cable is sheathed, 72 inches if sheathed and passing through a metal-protected bulkhead). Banks rated >500 Ah at 12 V (or proportional energy at higher voltages) require a per-battery OCPD.
Why it matters: The recommended bank capacity from this calculator drives whether you fall under the 500 Ah per-battery-OCPD rule. At 24 V, the threshold is 250 Ah; at 48 V, 125 Ah. Plan the OCPD bill of materials accordingly.
CSA C22.1 §16-200 (Canadian Electrical Code, 2024 edition)
Stationary battery systems for residential or commercial standby must be installed in a dedicated, ventilated, accessible enclosure with the battery disconnect within sight of the bank. Lead-acid banks rated >50 Vdc require spill-containment provisions.
Why it matters: Off-grid Canadian installations sized with this tool need to plan enclosure, disconnect, and (for flooded/AGM/Gel banks above 50 Vdc) electrolyte containment up front — these aren't aftermarket additions.
NEC 706 (Energy Storage Systems, 2023 edition)
Energy storage systems above 1 kWh in a dwelling unit must include a disconnect within sight of the ESS and meet UL 9540 (system-level) or UL 1973 (battery-level) certification. Working space ≥30 in front, ≥36 in for >150 V to ground.
Why it matters: Any LFP bank this calculator recommends above 1 kWh stored energy in a dwelling triggers NEC 706. A 200 Ah 12 V LFP bank = 2.56 kWh = NEC 706 applies; pick certified batteries up front to avoid a permit failure.

Citations are paraphrased for brevity. Always work from the most recent published edition of each standard for permit submittals.