What is ‘Depth of Discharge’ (DoD) and Why it Matters for Battery Life

You’ve seen it before. You buy a 128GB phone only to find that 20GB is already taken by system files you can’t touch. It’s frustrating. You didn’t get the full capacity you paid for. Solar batteries have a similar concept, and understanding it is the single most important factor in choosing the right one for your home.

This concept is called Depth of Discharge (DoD). It’s a simple percentage that answers one critical question: Of all the energy your battery can physically hold, how much can you actually use every day without damaging your investment?

Getting this right is the key to unlocking years of reliable performance and lower electricity bills. We’re going to break it down without the jargon, so you can see exactly how much power you'll have to run your home.

"The number on the box isn't the number that powers your home. Depth of Discharge is the bridge between the two."

The Two Numbers That Define Your Battery's Power

When you look at a battery's spec sheet, you’ll see its size listed in kilowatt-hours (kWh). This is its Nominal Capacity—the total amount of energy the battery can chemically store. Think of this as the size of the fuel tank.

But the number that actually matters for your daily savings is the Usable Capacity. This is the energy you can safely access, and it's determined by the battery's maximum Depth of Discharge (DoD).

Let's use a real-world example:

A SolaX T-BAT H 5.8 battery has a nominal capacity of 5.8 kWh. Specifically, the Triple Power T-BAT H 5.8 offers a Nominal Capacity of 5.8 kWh and a Usable Capacity of 5.1 kWh. However, it's engineered with a 90% DoD to ensure a long and healthy life.

The simple math is:
5.8 kWh (Nominal Capacity) x 90% (DoD) gives you 5.1 kWh of Usable Capacity.