Off-Grid Battery Bank Calculator

Size a battery bank from daily watt-hours, autonomy days, system voltage, chemistry depth of discharge, inverter efficiency, battery module size, load demand, and recharge target.

⚡Off-Grid Presets

🔧Battery Bank Inputs

Daily energy use (Wh/day) Total daily load energy at the AC outlets or DC load terminals.

Autonomy days Days the bank should run without meaningful recharge.

System voltage Higher voltage lowers DC current for larger inverter loads.

Battery chemistry and usable DoD Usable depth of discharge converts stored energy into usable energy.

Inverter efficiency (%) Common pure sine inverter range is about 85% to 94%.

Battery module size Used to calculate batteries in series and parallel strings.

Max continuous AC load (W) Checks DC current and practical system voltage headroom.

Recharge target (hours) Hours available to replace one day of energy use.

This calculator sizes nominal storage. Confirm battery manufacturer limits for charge current, discharge current, series wiring, parallel wiring, temperature range, and inverter compatibility.

Nominal Bank Capacity

0 Ah

0 kWh stored

Battery Count

0S x 0P

Usable Energy

0 kWh

0 days at entered load

Recharge Target

0 W

0 A continuous DC draw

Full Sizing Breakdown

🔋Battery Chemistry Spec Grid

80-90%

LiFePO4 usable DoD

Flat voltage, high cycle life, low maintenance, strong fit for RV and cabin banks.

50%

AGM practical DoD

Sealed lead acid option; heavier and needs more nominal Ah for the same usable energy.

C/5-C/8

Lead acid charge pace

Bulk charging is current-limited and absorption time slows full recovery.

0.5C-1C

Lithium load range

Many lithium packs allow higher current, but BMS limits still control usable output.

📊Chemistry Comparison Table

Chemistry	Typical usable DoD	Nominal voltage examples	Best fit
LiFePO4	80% to 90%	12.8 V, 25.6 V, 51.2 V	Frequent cycling, cabins, RVs, backup systems
AGM lead acid	About 50%	12 V blocks	Simple standby banks with moderate discharge depth
Flooded lead acid	About 50%	6 V golf cart, 12 V marine	Serviceable banks where ventilation and watering are planned
Gel lead acid	About 50%	12 V blocks	Low current sealed banks with careful charge voltage control
Lithium titanate	About 80%	24 V and 48 V packs	Cold or high-cycle specialty systems

⚙Voltage and Load Planning Table

System voltage	Common load range	Approx DC amps at 2,000 W	Planning note
12 V	Under 1,500 W	185 A at 90% efficiency	Useful for small RV loads; cable current rises quickly.
24 V	1,000 W to 3,000 W	93 A at 90% efficiency	Good middle ground for cabins and compact solar systems.
48 V	2,000 W and higher	46 A at 90% efficiency	Preferred for larger inverter loads and longer DC cable runs.
Series strings	Match target voltage	Battery volts add	Four 12.8 V modules in series make a 51.2 V nominal string.

🏠Common Off-Grid Bank Sizes

Use case	Daily energy	Autonomy	Typical bank target
Weekend RV lights, pump, fridge controls	800 to 1,500 Wh/day	1 to 2 days	12 V 200 to 300 Ah lithium
Small cabin with DC fridge and laptop	2,000 to 3,500 Wh/day	2 days	24 V 250 to 400 Ah lithium
Remote work cabin with Starlink-class internet	4,000 to 6,000 Wh/day	2 to 3 days	48 V 250 to 400 Ah lithium
Home backup essentials	6,000 to 10,000 Wh/day	1 to 2 days	48 V 300 to 600 Ah lithium

☀Recharge Target Reference

Daily load	4-hour recharge	5-hour recharge	6-hour recharge
1,500 Wh/day	417 W plus losses	333 W plus losses	278 W plus losses
3,000 Wh/day	833 W plus losses	667 W plus losses	556 W plus losses
6,000 Wh/day	1,667 W plus losses	1,333 W plus losses	1,111 W plus losses
10,000 Wh/day	2,778 W plus losses	2,222 W plus losses	1,852 W plus losses

💡Battery Bank Sizing Tips

Measure watt-hours first. A battery bank sized from nameplate watts alone can be badly oversized or undersized. Use watt-hours per day from a meter, inverter log, solar charge controller, or a realistic appliance-by-appliance load list.

Series and parallel both matter. Series batteries raise voltage while Ah stays the same. Parallel strings raise Ah while voltage stays the same. The calculator rounds up full strings so the bank voltage remains usable.

In order to determine the size of a battery bank that is necessary for you’re off-grid power systems, you must calculate the amount of energy that your off-grid system use every day. The amount of energy that off-grid systems use every day is the most important number in creating a battery bank, as the amount of energy that is used every day will determine the capacity of the battery bank. For instance, off-grid systems with small appliances like an refrigerator with LED lights and a laptop charger may use around three thousand watt-hours of energy every day.

Adding appliance like a water pump to the energy use of the off-grid system will increase the amount of energy that that system use every day. After determining the amount of energy that the off-grid system uses every day, you must also decide how many day you would like the battery bank to provide power to the off-grid system without requiring that it is recharged. This number of days that the battery bank will provide power to the off-grid system is referred to as the autonomy of the battery bank, and establishing a number of days of autonomy for the battery bank will provide a safety margin for the battery bank that cant be recharged.

How to Size a Battery Bank for Off-Grid Power

The chemistry of the batteries that you will use in the battery bank is a factor to consider in determining the size of that battery bank. Different chemistry batteries has different limits to the amount of energy that can be used from the battery bank. For instance, lithium iron phosphate batteries allow for eighty or ninety percent of the battery capacity to be used from the battery bank, but lead acid batteries only permit for fifty percent of the battery banks capacity to be used.

Because more of the capacity can be used from the lithium iron phosphate batteries, fewer of these batteries will be required to provide the energy that the off-grid system requires. Lead acid batteries, however, require that less of the battery bank’s capacity be used to ensure that the lead acid batteries do not break after a few season of use. Battery banks with chemistries that permit deep discharge require careful management of the battery bank to avoid over-discharging the battery bank.

Another factor to consider for the size of the battery bank is the voltage of the system. Off-grid systems with twelve volt batteries are suitable for small loads of electrical device. For larger loads, however, twenty-four volt or forty-eight volt systems is recommended.

Higher voltages permit for the current in the system to be reduce. Reducing the current in the system permits for the wires to be thinner and for the wires to generate less heat within the system. The charge speed of the charging source is another factor to consider.

If you desire for your battery bank to be recharged quickly, your battery bank will need to recieve more power from the charging source than the amount of energy that the off-grid system uses each day. Because of energy loss during the battery bank charging process, the charging source will have to provide additional power to the battery bank to make up for the energy used by the off-grid system. Should the charging source be too small to provide enough energy to the battery bank, the battery bank will remain low on energy even while the sun is shine on the solar panels that charge the battery bank.

Additionally, another factor to consider is how the weather impact the charging source of the battery bank. For instance, the energy provided by solar panels is reduced in cloudy weather, and the capacity of lithium batteries are reduced in cold weather. The layout of the battery bank is another factor to consider.

Batteries can be connected in series to increase the voltage of the system, or the batteries can be connected in parallel to increase the total capacity of the battery bank. Additionally, another factor to consider is the voltage drop that can occur in the cables that connect the batteries. If the cables are long, the voltage drop that occurs in the system may lead to a loss of power to the off-grid system.

To avoid this potential loss of power, many off-grid system builders will add a safety margin to the size of the battery bank that is constructed for the off-grid system. Thus, the goal in building the battery bank is to provide enough energy to the off-grid system to power the essential loads, yet to include enough extra capacity to the battery bank to ensure that the energy is not constantly being monitor for its level of charge.