How Many Batteries Is Needed For 3000 Watt Power Inverter

3000-watt power inverters are a very popular class of power inverters used during blackouts, emergencies, camping, for off-the-grid, medical and security systems, and similar.

Most 3000-watt power inverters are very simple to use, however, dimensioning required batteries or battery packs can cause some issues in terms of reliability and runtime.

Published: January 24, 2022.

3000 Watt Power Inverters Energy and Power Requirements

Power inverters are not ideal units and have a certain energy loss during energy conversion.

Good power inverters feature an energy efficiency of ~85%, although there are units with better energy efficiency - such units are usually more expensive ones.

Thus, if the power inverter features a continuous output power of 3000 Watts, the required battery power is:

P_Bat = P_Inv / Energy Efficiency % = 3000 Watt / 0.85 = 3530 Watts

Also, power inverters usually feature a surge output power that is ~2x larger than the continuous output power, thus requiring the battery to provide much more power for a very short time (usually just a few seconds):

P_Bat = P_Int / Energy Efficiency % = 6000 Watt / 0.85 = 7060 Watts

Thus, if we want to power 3000 Watt power inverter that features energy efficiency of 85%, the battery (or battery pack) must be able to provide ~3600 watts continuously and ~7200 surge watts.

This solves power requirements. But, what about energy requirements?

Power inverters usually don't operate at full power all the time - if that is happening, then the power inverter is seriously underpowered.

Energy requirements are usually given in the form of continuous power during a certain time, for example, 1000W for 3 hours.

In that case, the energy that the battery must provide is calculated using these formulas:

P_Bat = 1000 W / 0.85 = ~1200 Watt

E_Bat = P_Bat * T (h) = 1200 Watt * 3 hours = 3600 Wh = 3.6 kWh

In this example, if we want to power a 3000 Watt power inverter with surge power of 6000 Watt and energy efficiency of 85%, we need a battery that is able to provide 3600 Watts continuously, 7200 surge Watts and that features an energy capacity of at least 3.6 kWh.

3000 Watt power inverters are usually 12V units, but there are also 3000 Watt power inverters that accept 24V, 36V, or even 48V.

Battery currents can be easily calculated:

I_BatCont = P(W) / U(V) = 3600W / 12V = 300 Amps

I_BatSurge = P(W) / U(V) = 7200W / 12V = 600 Amps

I_BatAverage = P(W) / U(V) = 1200W / 12V = 100 Amps

Note: as one can see, when powering 3000W inverters using 12V batteries, currents are rather strong!

Battery actual capacity can be calculated using following formula:

Actual Capacity = Required Energy (Wh) / U(V) = 3600 Wh / 12V = 300 Ah

Actual Capacity vs. Nominal Capacity: nominal capacity of the battery is battery capacity measured when the battery is discharged for 20h. However, when the battery is discharged faster, especially lead-acid batteries, actual capacity decreases - 1h actual capacity can be as little as 50-70% of nominal (20h) capacity for lead-acid batteries.

Lithium deep discharge batteries are less sensitive to discharge current in terms of capacity loss, but if a certain current is reached, the built-in Battery Management System (BMS) disconnects the lithium battery to protect it from overcurrent discharge.

Personally, for most applications lithium batteries are a much better choice than lead-acid batteries - for more about these batteries, feel free to check out our Best 12V, 24V, 36V, and 48V Lithium Deep Cycle Battery For a Power Inverter article.

For example, Ampere Time 12V 300Ah battery is one of the best batteries in its class and supports:

- maximum continuous current of 200 Amps,

- maximum surge current of 400 Amps for 5 seconds,

- connections of four batteries in series and four batteries in parallel in order to create larger battery packs.

In order to power 3000W power inverter in our example, we would need at least two such batteries connected in parallel - such battery pack would support:

- maximum continuous current of 400 Amps, which is more than the required 300 Amps,

- maximum surge current of 800 Amps for 5 seconds, which is more than the required 600 Amps,

- actual capacity is 600 Ah, which is more than the required 300 Ah.

If such battery pack is too large, note that Ampere Time 12V 200Ah battery features the same current limits, but provides an actual capacity of 400 Ah when two batteries are connected in parallel - still more than enough for our example.

Of course, there are other 12V lithium batteries that can be used to power 3000W and similar power inverters:

When calculating the number of required batteries in order to power 3000 Watt power inverter, it is a good practice to over-dimension the battery pack - in most situations, energy requirements can only grow...

And whatever You do, stay safe - these units are easy to use and maintain, but they are not toys and can provide huge currents that can do some serious damage, injuries, or worse...