Battery storage vs a backup generator for commercial facilities
A generator supplies power when the grid fails. A commercial battery works on your electricity bill while the grid is up, and can also provide backup when designed for it. Some facilities benefit from both.
01
A generator mostly waits
A standby generator is built for outages and needs regular testing. Emergency engines generally cannot be used for routine peak shaving, so their main job is keeping the site running when the grid fails.
02
A battery works on the bill
A battery can reduce demand charges by supplying stored energy during billed peaks. Eligible battery systems can earn utility program payments. It does this without burning fuel on site.
03
Backup is an option
Backup power is an option: with the right inverter configuration and electrical design, the battery keeps designated critical loads running during an outage. If backup matters to you, we scope it into the design.
Battery storage vs a generator at a glance
Compare the job each system does, how long it can run and what it needs to keep working.
| Battery storage | Standby generator | |
|---|---|---|
| Main job | A battery can reduce demand charges by supplying stored energy during billed peaks. Eligible battery systems can earn utility program payments. | Standby power during outages |
| Earns money with the grid up | Peak shaving when the load and tariff support it. Eligible battery systems can earn utility program payments. | Emergency engines generally cannot be used for routine peak shaving or paid non-emergency demand response[1] eCFR, 40 CFR 60.4211(f) (opens in a new tab) |
| Switch-over in an outage | Depends on the inverter and electrical design, scoped per site when backup is designed in | Up to 10 seconds for a Type 10 emergency system[2] NFPA, An Overview of NFPA 110 (opens in a new tab) |
| Runtime in an outage | Hours, set by the energy held in reserve and the size of the critical load; longer with solar to recharge | As long as there is fuel on site or on the way |
| Fuel and emissions | No fuel on site and no exhaust | Burns diesel or natural gas; 10.21 kg of CO₂ per gallon of diesel[3] U.S. EPA, GHG Emission Factors Hub (opens in a new tab) |
| Upkeep | Monitored remotely; no fuel to store, test or replace | Weekly inspection, monthly exercise and periodic load tests; fuel storage and replacement[2] NFPA, An Overview of NFPA 110 (opens in a new tab) |
| Permits | Electrical and fire review, applicable building and fire approvals, and utility interconnection[4] NFPA 855, Standard for the Installation of Stationary Energy Storage Systems (opens in a new tab) | Building and electrical permits, engine emission rules and often an air permit or registration; fuel storage rules |
When the grid goes down
Slide the outage length. A generator takes seconds to pick up the load and then burns fuel for as long as it runs. A battery with backup designed in picks it up without starting an engine, with a switch-over that depends on the design, and carries it as far as its reserve goes.
Type 10 diesel backup system
Runs as long as there is fuel
- Switch-over
- ≤ 10 s
- Diesel burned
- 14 gal
- CO₂ emitted
- 146 kg
Battery with backup
300 kWh held in reserve
- Switch-over
- Depends on design*
- Fuel burned
- 0 gal
- Carries the load for
- 2 hours
2 hours without the grid: the battery carries the 100 kW of critical load the whole way, with no fuel burned. The generator would burn about 14 gallons of diesel.
Illustrative site: 100 kW of critical load. The generator is assumed to make about 14 kWh per gallon; CO₂ uses EPA's 10.21 kg per gallon of diesel. *Battery switch-over depends on the inverter and electrical design, and backup is scoped per site.
And while the grid is up
A standby generator mainly waits for an outage, apart from its tests. A battery can work on the bill throughout the year. This illustrative calendar shows one possible pattern.
Battery
Working on 261 days
- Shaving the peak
- Peak + program event
- Standing by
Standby generator
Running on 13 days
- Monthly test run
- Outage
- Idle
Illustrative year. Which programs a battery can join, and how many event days they call, depend on the utility and the site.
It does not have to be either-or
A generator and a battery answer different questions: how long can we run without the grid, and how much does the grid cost us. Plenty of sites need both answers.
01
Keep the generator for long outages
Where code requires a generator, or the site has to ride through days without the grid, keep it. A battery does not replace that.
02
Let the battery earn the rest of the year
The battery can reduce grid demand during billed peaks. With backup designed in, it can also carry critical loads through shorter outages without starting the engine.
03
Size the reserve on purpose
Every kWh held back for outages is a kWh that cannot shave a peak. How much to reserve is a design decision for each site, made with the savings in view.
Explore your options
Questions about batteries and generators
We already have a generator. Should we use a battery instead?
Usually alongside it, not instead. They do different jobs: the generator waits for outages, and the battery can lower the bill while the grid is available. With backup designed in, a battery can carry critical loads through shorter outages with no fuel to burn. For outages that last days, or where code requires a generator for life safety, keep the generator. Many facilities keep both.
Will a battery keep us running in an outage? For how long?
It can. Backup power is an option: with the right inverter configuration and electrical design, the battery keeps designated critical loads running during an outage. If backup matters to you, we scope it into the design. How long depends on two numbers: how much energy is held in reserve, and how much load it has to carry. Backing up only critical loads stretches the reserve. A bigger reserve lasts longer but leaves less energy for cutting peaks, so the reserve is sized per site with both in view.
Why not use our generator to shave peaks?
Federal rules allow emergency operation without a time limit. Maintenance and readiness testing generally have a 100-hour annual allowance; up to 50 hours of other non-emergency operation count within it, and those hours generally cannot be used for peak shaving or paid non-emergency demand response. Routine peak shaving calls for an engine and permits that allow non-emergency use.
How much could a battery earn us compared with a generator sitting idle?
It is hard to know without a full analysis of your interval data, rate and programs, and it varies a lot from site to site. As a rough first look, annual savings come to about 1–4 months of your electric bill. A standby generator generally earns nothing on the bill. Costs for either vary widely by site, so a full analysis comes before any proposal.
How long does a battery take to install?
Typically live in 3–6 months. Most of that time is design, permitting and utility interconnection, which EQORE handles. If backup is part of the design, it is scoped and permitted at the same time.
Sources (4)· Last reviewed October 26, 2026
- eCFR, 40 CFR 60.4211(f) (opens in a new tab), emergency operation, maintenance/testing and restricted non-emergency use; retrieved October 26, 2026
- NFPA, An Overview of NFPA 110 (opens in a new tab), Type 10 restores power within 10 seconds; weekly, monthly and 36-month tests (January 2023)
- U.S. EPA, GHG Emission Factors Hub (opens in a new tab), 10.21 kg of CO₂ per gallon of diesel (January 2025)
- NFPA 855, Standard for the Installation of Stationary Energy Storage Systems (opens in a new tab)
Take control of your power
Find out what a battery would earn at your site
Send a recent electricity bill, and tell us which loads must stay on in an outage. We model your peaks against a year of interval data and show system options, projected savings and payback, with backup scoped in if you need it.