Should I use 12V, 24V, or 48V for my battery bank?

Stay at 12V for small systems under 2 kWh and most camper builds (huge appliance ecosystem, cheap fuses and breakers). Move to 24V when your inverter is 2-3 kW, and 48V when total energy crosses 5 kWh. Higher voltage means smaller cables and lower DC current at the same power, which is cheaper and safer at scale.

How much does temperature affect battery capacity?

Capacity drops in the cold. At 0°C, expect about 85% of rated Ah. At -10°C, around 70% for most chemistries. LiFePO4 also cannot be charged below 0°C without a built-in heater - charging cold cells damages them permanently. Pick a heated battery or an insulated location if you operate in winter.

How many days of autonomy should I plan for?

For mobile setups (camper, boat) with active solar, 1-2 days is typical. For stationary off-grid cabins, 3-5 days is common to ride out storms. More days means a bigger, more expensive bank - usually it is cheaper to add solar than batteries past 2 days of autonomy.

What about round-trip efficiency?

Some of the energy you put into the battery is lost to heat during charge and discharge. LiFePO4 round-trip is around 95%, AGM and gel about 85%, flooded lead-acid 80%. The calculator divides daily demand by this efficiency so the bank actually stores enough usable energy.

Battery Bank Sizer for 12V, 24V, 48V Systems (LiFePO4, AGM)

Battery Bank Sizer

Daily EnergyWh

0Wh10kWh

Days of Autonomyd

0.5d7d

System Voltage

Battery Chemistry

Advanced settings

Result

Heads up: Parallel string count is high. Consider larger modules or a higher system voltage to reduce balancing complexity.

Recommended Bank

500 Ah

@ 12V

Total Capacity

6.00

kWh

Configuration

1S5P

5 × 100Ah 12V

Runtime

55.1 h

avg load

Cycle Life

~3500

cycles

Effective demand: 2105 Wh/d · 95% roundtrip · 80% DoD

Bank

500Ah

Energy

6.0kWh

Config

1S5P

Runtime

55.1h

Battery Chemistry Comparison Table

Pick the chemistry that fits your budget, weight, and cycle-life needs. LiFePO4 is the off-grid default today. Lead-acid types still make sense as a low-budget starter or for occasional-use boats.

Chemistry	Recommended DoD	Round-trip eff.	Approx cycles	Best fit
LiFePO4	80%	95%	~3500	Long-term off-grid, mobile, marine
AGM	50%	85%	~600	Mid-budget, sealed, vibration-prone
Gel	50%	85%	~800	Marine, deep cycle, sealed
Flooded lead-acid	50%	80%	~400	Lowest cost, occasional use, ventilation OK

Frequently Asked Questions

How do I size a battery bank for my off-grid system?

Multiply your daily energy demand (Wh) by the number of days of autonomy, then divide by the depth-of-discharge limit for your chemistry (80% LiFePO4, 50% lead-acid). Divide by system voltage for Ah. The calculator handles round-trip efficiency and temperature derating automatically.

What size LiFePO4 battery do I need for a camper?

A typical 1500-2500 Wh/day camper with 1 day autonomy needs around 200-300 Ah at 12V. Double for 2 days. Cold weather drops usable capacity, so insulate or pick heated batteries for winter.

What is depth of discharge (DoD)?

How much of the rated capacity you actually use before recharging. LiFePO4 handles 80% DoD comfortably. Lead-acid should stay under 50% DoD to last more than a few hundred cycles.

Should I go 12V, 24V, or 48V?

12V for systems under 2 kWh. 24V for inverters in the 2-3 kW range. 48V above 5 kWh. Higher voltage means smaller cables and 4x lower DC current at 48V vs 12V.

How does temperature affect battery sizing?

Capacity drops in cold. ~85% at 0°C, ~70% at -10°C. LiFePO4 cannot charge below 0°C without a heater - pick a heated battery or insulate.

How many days of autonomy should I plan?

Mobile (camper, boat): 1-2 days. Stationary off-grid: 3-5 days. Past 2 days, adding solar usually beats adding batteries on cost per kWh.

What is round-trip efficiency?

Energy lost to heat during charge and discharge. LiFePO4 ~95%, AGM/gel ~85%, flooded ~80%. The calculator divides demand by this so the bank stores enough usable energy.

Can I mix series and parallel?

Yes. Series for higher voltage, parallel for higher capacity. Keep all modules identical (brand, age, capacity). Stay under 4 parallel strings for clean balancing.

How to Calculate Your Battery Bank Size

Sizing a battery bank correctly is the single biggest cost decision in an off-grid build. Undersize and you run out of power before sunrise. Oversize and you spend hundreds or thousands more than you need to.

Step 1 - Add up daily Wh

Walk through every appliance you run on the battery. Multiply each by the hours per day it actually runs. A 60W fridge running 8 hours equivalent is 480 Wh/day. A 5W LED light for 4 hours is 20 Wh/day. Sum the lot.

Step 2 - Account for losses

Energy comes off the battery less efficiently than it goes in. LiFePO4 is around 95% round-trip; lead-acid about 80%. The calculator divides your demand by this efficiency so the bank actually stores enough.

Step 3 - Pick days of autonomy

How many full days do you want to run without recharging? Mobile setups (camper, boat) usually pick 1-2 days, relying on regular solar input. Off-grid cabins commonly aim for 3-5 days to ride out storms.

Step 4 - Apply DoD limit

Divide the usable Wh by the chemistry's DoD limit. LiFePO4 80% lets you draw 80% of rated capacity. Lead-acid types should be capped at 50% DoD to keep cycle life acceptable.

Step 5 - Convert to Ah at your system voltage

Total Wh divided by system voltage gives required Ah. The calculator rounds up to a buyable module size and returns a series/parallel layout that matches.

Battery Bank Sizer

Battery Bank Sizer

Result

Battery Chemistry Comparison Table

Frequently Asked Questions

How to Calculate Your Battery Bank Size

Step 1 - Add up daily Wh

Step 2 - Account for losses

Step 3 - Pick days of autonomy

Step 4 - Apply DoD limit

Step 5 - Convert to Ah at your system voltage

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