Deep Cycle Battery Capacity Calculator

Size a deep-cycle battery bank for smart home backup, solar storage, network racks, cameras, pumps, refrigerators, and inverter loads using watts, runtime, voltage, chemistry, depth of discharge, and reserve.

📌Real Backup Presets

🔋Battery Capacity Inputs

Average connected load (watts)

Use measured average watts for runtime capacity. Surge is checked separately.

Required backup runtime (hours)

This is the load-side runtime target before battery reserve is applied.

Target bank voltage

Higher voltage reduces current for the same watt load.

Nominal voltage per battery

The calculator estimates the required series count from this value.

Capacity per battery (Ah)

Use the 20-hour rating for lead-acid when available.

Battery type and planning depth

Depth of discharge is limited to protect cycle life and usable reserve.

Inverter or DC path efficiency (%)

Use 95 to 98 for direct DC, 85 to 92 for many AC inverter loads.

Extra reserve buffer (%)

Reserve covers aging, cold weather, inverter overhead, and load growth.

Capacity Results

Required Nominal Energy 0 Wh Battery-side gross capacity

Required Bank Capacity 0 Ah At the actual bank voltage

Recommended Battery Count 0 Series and parallel layout

DC Current Estimate 0 A Battery-side running current

⚙Deep Cycle Spec Grid

Wh Watt-hours are the core energy unit for capacity sizing.

Ah Amp-hours become meaningful only with battery voltage.

50% Typical planning DoD for AGM and flooded lead-acid.

85% Common practical DoD for LiFePO4 home backup banks.

90% Typical inverter efficiency near moderate load.

1.10x Default reserve multiplier for extra capacity margin.

24 V Good middle ground for medium smart home loads.

48 V Better current control for larger inverter loads.

📐Battery Type Comparison

Flooded Lead-Acid

Best modeled near 50% DoD for long life. Capacity falls with high current, cold locations, and older plates.

AGM Deep-Cycle

Useful for enclosed backup cabinets and UPS-style loads, but runtime should still stay conservative at higher discharge rates.

Gel Deep-Cycle

Similar capacity math to AGM, with tighter charge and current limits that should be checked against the battery datasheet.

Lead-Carbon

Often tolerates partial-state cycling better than standard lead-acid, so a 60% planning depth is a reasonable model.

LiFePO4

Higher usable depth and flatter voltage make LiFePO4 efficient for home backup capacity when BMS current limits are adequate.

Small SLA

Small sealed batteries lose usable capacity quickly under heavy loads, so this calculator gives them a shallower DoD model.

📊Reference Tables

Battery Type	Planning DoD	Typical Efficiency	Best Capacity Use
Flooded lead-acid deep-cycle	40% to 50%	75% to 85%	Solar shed storage and ventilated utility banks with careful maintenance.
AGM sealed deep-cycle	40% to 50%	80% to 88%	Indoor backup cabinets, router shelves, UPS-style smart home loads.
Gel sealed deep-cycle	45% to 55%	82% to 88%	Low-current standby systems where strict charging limits are followed.
Lead-carbon deep-cycle	50% to 60%	83% to 90%	Frequent partial cycling in small solar and automation banks.
LiFePO4 deep-cycle	80% to 90%	92% to 98%	High-use home backup, network racks, camera loads, and inverter banks.
Small sealed SLA	30% to 40%	75% to 85%	Short runtime electronics backup where high-rate discharge is modest.

Smart Home Load	Typical Average Watts	12-Hour Energy	Capacity Note
Fiber ONT, modem, and WiFi router	25 to 45 W	300 to 540 Wh	Excellent fit for direct DC backup or a very small efficient inverter.
Security panel, LTE radio, and smart hub	15 to 40 W	180 to 480 Wh	Low steady load rewards accurate watt measurement and reserve planning.
PoE switch, cameras, and NVR	120 to 300 W	1.44 to 3.6 kWh	Night infrared LEDs can push camera loads above daytime averages.
Mini fridge or efficient refrigerator average	60 to 150 W	720 Wh to 1.8 kWh	Capacity uses average watts, while inverter sizing must handle startup surge.
CPAP with humidifier reduced or off	25 to 60 W	300 to 720 Wh	Check the actual nightly watt draw because humidifier heat changes runtime.
Sump pump on duty-cycle average	200 to 700 W	2.4 to 8.4 kWh	Use duty-cycle average for capacity and running surge for equipment limits.

Bank Voltage	Current At 100 W	Current At 500 W	Current At 1,000 W
12 V nominal bank	8.3 A before losses	41.7 A before losses	83.3 A before losses
24 V nominal bank	4.2 A before losses	20.8 A before losses	41.7 A before losses
36 V nominal bank	2.8 A before losses	13.9 A before losses	27.8 A before losses
48 V nominal bank	2.1 A before losses	10.4 A before losses	20.8 A before losses

Example Project	Average Load	Runtime Target	Practical Battery Starting Point
Internet-only outage backup	35 W	12 hours	12 V 50 Ah LiFePO4 or 12 V 100 Ah AGM with reserve.
Security cabinet and smart hub	30 W	24 hours	12 V 100 Ah LiFePO4 or two 12 V 100 Ah AGM batteries in parallel.
PoE camera corner with NVR	160 W	10 hours	24 V 100 Ah LiFePO4 bank or larger lead-acid bank for 50% DoD.
Mini fridge average backup	90 W	18 hours	24 V 100 Ah LiFePO4 with inverter surge headroom.
Home essentials inverter bank	500 W	8 hours	48 V 100 Ah LiFePO4 bank or multiple AGM strings with heavy cabling.

✅Capacity Tips

Separate capacity from surge. Amp-hours and watt-hours estimate runtime from average watts. Inverter rating, BMS limit, fuse size, and cable sizing must also support startup and peak current.

Do not compare Ah without voltage. A 24 V 100 Ah bank stores twice the nominal energy of a 12 V 100 Ah bank, even though the Ah number looks identical.

This calculator estimates steady-state deep-cycle battery capacity. Confirm manufacturer ratings, discharge curves, charge limits, protection devices, and local electrical requirements before building a battery system.

When the power goes out, many peoples internet, security cameras, and medical device cease to function. Many individuals attempt to use small power strip or uninterruptible power supply (UPS) to provide power to these devices during the outage. However, these small power strips and uninterruptible power supplies will only provide power for short period.

In order to provide power for many hour during the outage, you must use deep cycle batteries. Deep cycle batteries are different than the types of battery that is used in an automobile. The deep cycle battery is specifically design to be drained over a long period.

How to Build a Simple Battery Backup for Power Outages

The automotive battery is designed to provide short bursts of energy. Batteries contain a measurement called amp-hours (Ah). The amp-hour measurement describe the capacity of the battery.

However, the amp-hour measurement does not give the total amount of energy that the battery can contain if the voltage of the battery isnt also given. For instance, 100 Ah of a battery at 12 volts contains a different amount of energy then a 100 Ah battery at 24 volts. The 100 Ah battery at 24 volts contains twice the amount of energy as the 100 Ah battery at 12 volts.

Therefore, watt-hours (Wh) are a better measurement of the total amount of energy that a battery can contain. With watt-hours you can calculate how many hour the battery will provide power to the devices based off the wattage that those devices use. Many people make the mistake of using the total capacity of the battery.

However, using the total capacity will damage the battery. Lead acid batteries, such as AGM and Gel batteries, will be damaged if they is deeply discharged. Lead acid batteries are chemically stress if they are discharged to 50% of their total capacity.

For this reason, the total depth of discharge for lead acid batteries should of be 50%. If a person purchases a 200 Ah lead acid battery, they should only use 100 Ah of the batterys total capacity. However, lithium batteries dont suffer from this same limitation.

Specifically, LiFePO4 batteries allow for deep discharges and contain nearly double the amount of usable capacity in comparison than lead acid batteries. Another consideration in building a backup system is the efficiency of the devices that convert the batterys energy to the power that the devices use. For instance, if an inverter is used to convert the batterys energy to the amount that the devices require, the inverter will use some of the energy from the battery.

Energy is lost in the inverter because some of the energy is convert to heat. Therefore, if you do not consider the energy loss from the inverter in building the backup system, the battery may become deplete of its power sooner than calculated. Another consideration with building a backup system with batteries is the voltage of the batteries.

Commonly, batteries are of 12 volts. However, using 24 volts or 48 volts will be more efficient. Higher voltages allow for lower currents to move the same amount of power.

Using lower currents in the wires will prevent the wires from becoming warm with high level of current. For these reasons, using a 12 volt battery for a device that uses a large amount of power will result in high currents in the wires. Using a higher voltage will prevent the wires from becoming to warm.

One more consideration in building a backup system is to include a buffer in the system. The performance of the hardware will change over time. Batteries have a limited amount of capacity over time.

Additionally, batteries lose their capacity when the temperature around the battery becomes cold. Another reason to include a buffer in the backup system is to account for potential increase in the power needs of the devices in the system. If you include a buffer in the system, say of 10 or 20% of the total power of the system, it will allow the system to continue to function even if the battery chemistry slow due to cold weather.

Building a backup system require consideration of the costs of the batteries. For instance, individuals can purchase the expensive LiFePO4 batteries that contain more usable power than lead acid batteries. Additionally, individuals can also purchase the less expensive lead acid batteries such as AGM batteries.

However, the AGM batteries will need to be replaced more frequently. Another consideration of the batteries is the difference between the capacity that the battery can provide and the surge of power that the battery can provide. While the capacity will determine how many hour of power the batteries will run, the surge will determine whether or not the battery and inverter can supply enough power to devices that contain compressors, like refrigerators.

By calculating the capacity of the batteries, the voltage, the chemistry of the batteries, and the surge power requirements of the devices, individuals can create a calculated plan for the power outages.