Figuring out how many batteries you need can be daunting. If you don’t have enough battery capacity, you run out of power and need to fire up the backup generator.

On the other hand, if you buy too many batteries, you add unnecessary expense to your system, with extra components, complexity and maintenance.

Sizing solar batteries is one of the first steps in designing your off-grid system. The amount of battery storage you need is based on your energy usage. Energy usage is measured in kilowatt hours (kWh) over a period of time.

For example: 1,000 watts x 10 hours per day = 10 kWh per day 

After estimating daily usage we need to consider which type of battery will work best, as they have unique performance characteristics and are sized differently.


There are a few different battery types commonly used for off-grid storage systems:

Price: $300-450 / KWh Storage
(Per Usable KWh Capacity)


  • Typical Lifespan: (10) Years
  • High Power Density
  • Small Footprint
  • No Maintenance
  • No Toxic Venting of Gas

Price: $300-450 / KWh Storage
(Per Usable KWh Capacity)


  • Typical Lifespan: (6) Years
  • Low Power Density
  • Medium Footprint
  • No Maintenance
  • No Toxic Venting of Gas

Price: $300-450 / KWh Storage
(Per Usable KWh Capacity)


  • Typical Lifespan: (2-3) Years
  • Low Power Density
  • Large Footprint
  • High Maintenance
  • Toxic Venting of Gas

The Two Main Categories are Lithium & Lead-Acid.

1.) Lithium Batteries are more efficient, lose less power in charge/discharge process, weigh less and have the highest power density. [Batteries in this category are Lithium-Ion, LiFePO4, and NMC.]

2.) Lead-Acid Batteries are less efficient, lose more power in charge/discharge process, weigh more and have a lower power density. [Batteries in this category are Flooded, Sealed, AGM, Gel, and Deep-Cycle Lead-Acid Batteries.]

The reason people used to buy “Lead-Acid” was because it was cheap however we are now offering “Lithium Batteries” at the same price per Usable/KWh that last (3x) as long and require no maintenance. Lead-Acid batteries have a limited amount of usable capacity and can be typically discharged to 50%.
Because of the better efficiency and deeper discharge depth, lithium battery banks only need to be HALF the size of a comparable lead-acid battery bank! Lead acid batteries are sensitive and need to be fully recharged every day where lithium batteries can stay at a partial charge without any adverse effect.

BigBattery was created to make Lithium Batteries affordable for everyone. We now offer New “Lithium Batteries” at the same price per usable/KWh that last (3X) as long and require no maitnenece. There is NO reason to buy Lead-Acid today. Lithium Batteries are clearly the better solution, BigBattery is manufacturing and supplying these batteries to you at the Best Price in the USA!
(We’ll beat any competitors price by 10% Guaranteed!)


The exact math for sizing your battery system is based on your daily power usage and the battery type.
Based on the usage of 10 kWh per day, Here are some examples:


10 kWh x 2 (for 50% depth of discharge) x 1.2 (inefficiency factor) = 24 kWh


10 kWh x 1.2 (for 80% depth discharge) x 1.05 (inefficiency factor) = 12.6 kWh

Battery capacity is specified either in kilowatt hours, or amp hours.

For Example: 24 kWh = 500 Ah at 48 V → 500 Ah x 48 V = 24 kWh

It’s usually a good idea to round up to help cover inverter inefficiencies, voltage drop and other losses. Think of this as the minimum battery bank size based on your typical usage. You may want to consider 600-800 amp hours of capacity, based on this example, depending on your budget and other factors.

Battery banks are typically wired for either 12, 24 or 48 volts depending on the size of the system. Here are examples of battery banks for both lead acid and lithium, based on an off-grid home using 10 kWh per day.


  • 2,000 Ah at 12 V
  • 1,000 Ah at 24 V
  • 500 Ah at 48 V


  • 1,050 Ah at 12 V
  • 525 Ah at 24 V
  • 262.5 Ah at 48V

Other factors that influence battery sizing:

  • Ambient Temperature – head or cold has a big impact on battery performance and capacity.
  • Seasonal Factors – people use more power at different times of the year. The sun produces more power in the summer than in the winter.
  • Budget – battery bank size is often a compromise between what you want to spend on batteries and how often you’l need to run your backup generator.

Use this information, based on your energy usage, to get an idea of the minimum battery bank size, and then call us at #(818) 280-3091 for help pricing the best battery for your needs.

This is not intended to be a comprehensive guide on off-grid design.

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