Commercial Battery Storage Buyer’s Checklist: Tesla, Collie, SMA, and Surge Protector Sizing

I manage purchasing for a 120-person professional services company with three locations. I don't design electrical systems, but I handle vendor selection for them. When a 2023 transformer failure knocked out our main office for nearly a full business day, I became the person who had to ask better questions about battery backup. This checklist is the practical version of those questions. It's written for other buyers who need to make smart procurement decisions without pretending to be electrical engineers.

Who should use this checklist

Use this when you're evaluating a lithium-based battery system for a commercial office, a fleet facility, or a solar-plus-storage project. The same questions apply whether the quote is for a few Tesla Powerwalls, a larger outdoor cabinet, or a containerized Collie battery energy storage system. The goal is to compare proposals on the details that actually determine whether the system will perform in five years.

Step 1: Define what actually needs backup power

Before comparing any brands, make a list of loads that must continue running during an outage. Our list turned out to be shorter than the vendor's original proposal suggested. We needed the network switch, file server, VoIP phone system, door access control, and one conference room video setup for remote executive calls. We did not need the coffee machines, most desktop workstations, or the HVAC system.

Ask yourself the same question before you let anyone quote you a system. It keeps the project honest and prevents you from paying for battery capacity you don't need.

Step 2: Ask for a battery health test, not just a capacity number

A raw kilowatt-hour number looks persuasive, but it doesn't tell you whether the battery has been properly maintained, stored, or cycled. This is where I started asking for a battery health test on every serious quote.

If the vendor is proposing a Tesla Powerwall or another Tesla-based storage product, ask for the diagnostic battery health report from the installer's toolset before you sign anything. Tesla's own self-test and service mode can produce a state-of-health estimate, but the important part is that you see it in writing. The same logic applies if you're buying a used Tesla home battery or accepting a refurbished unit as part of a smaller commercial project. In the vehicle world, a Tesla battery health test has become a common used-car check; stationary storage deserves the same kind of scrutiny.

For any battery supplier, request these four items:

• State of health percentage reported by the battery management system
• Cycle count or equivalent full cycles
• Total energy throughput in megawatt-hours
• The temperature range during storage or prior operation

Honestly, I'm not sure why so many commercial battery quotes skip this information. My best guess is that it's easier to sell a battery as an appliance than as a device with a measurable health profile.

Step 3: Compare Tesla vs Collie BESS on the same spec sheet

There is a natural temptation to choose a familiar name. Tesla has strong brand recognition and integrated software, especially for solar customers. But when a vendor included a Collie battery energy storage system in a competing quote, I had to compare them on paper rather than by brand reputation.

Here is the template I use:

• Usable energy, not just rated energy capacity
• Maximum continuous discharge power
• Startup or transfer time if the system is used as backup
• Round-trip efficiency
• Operating temperature range
• Communication protocol such as Modbus or local API access
• Safety certifications relevant to your region

Some quotes say “100 kWh battery system.” That could mean 100 kWh of raw cells or 100 kWh of usable energy, and those are very different. I went back and forth between a Tesla proposal and a Collie proposal for two weeks. Tesla's monitoring software was impressive, but the Collie quote offered a warmer operating range for our unconditioned equipment shed. On paper, the Tesla was easier to manage. The Collie system was a better physical fit for our site.

Step 4: Check the power conversion and inverter path

A battery is not useful if the system cannot convert DC power safely into the AC power your building uses. Some storage products include an integrated inverter, while others use a separate inverter. When the design uses a separate power conversion unit, a brand like SMA comes up often because of its track record in commercial solar and storage installations.

An SMA power inverter is not mysterious, but it does add a spec layer to review. Ask for the inverter's continuous output rating, surge capacity, grid certification, and off-grid capability if that matters to you. Not every inverter is designed to run a building independently during a prolonged outage. Some are only designed for solar export or self-consumption.

If you're pairing battery storage with an existing solar array, also ask whether the inverter can handle the DC-to-AC ratio correctly. A 30 kW solar array on a 25 kW inverter is common, but you need the inverter's DC input limits documented before you approve the design.

Step 5: Size the surge protector the right way

When someone asks me how to size a surge protector for a battery project, I tell them to start with system voltage and installation location, not with the size of the electrical load. That still confuses people, but it's true. A surge protector does not carry the building load during normal operation. It shunts transient overvoltage to ground, so you size it for the voltage class and the expected surge environment.

For a commercial battery and inverter installation, use this basic process:

1. Identify the system voltage and phase configuration of the AC connection point.
2. Choose a surge protective device type based on where it will be installed. For a service entrance or main distribution panel, use a Type 1 or Type 2 device listed under UL 1449.
3. Select a device with a maximum continuous operating voltage that properly exceeds your nominal system voltage.
4. Check the surge current rating in kA per mode. A typical distribution panel installation might use a device rated at 20 kA to 50 kA per mode, but the actual requirement depends on the site's risk and the local electrical code.

The common mistake is to ask for the surge protector based on the battery's kilowatt rating. That is not how a transient protector is selected. A larger battery does not automatically require a larger surge protector in the way that a larger motor requires a larger circuit breaker.

Step 6: Trust suppliers who admit what they can't do

The best signal in any proposal is honesty about limitations. The vendor who told us, “This system can keep your network and phones up for four hours, but it won't cool the whole building,” became more believable than the vendor who promised full backup and made it sound simple.

Good specialists know where their product stops being the right answer. A residential-style Tesla home battery may be a fine solution for a small branch office with a few loads, but it can become the wrong tool for a building with an elevator or a large motor load. If a supplier tells you to buy a separate uninterruptible power supply for a sensitive piece of medical or IT equipment instead of relying only on the battery system, that's an honest sign. I would rather work with a specialist who knows their limits than a generalist who overpromises and disappears after commissioning.

Final notes for purchasing teams

Do not let a brand name carry the whole proposal. Whether the quote is built around Tesla, a Collie battery energy storage system, an SMA power inverter, or a combination of all three, the acceptance criteria matter more than the logo.

Before you issue a purchase order, ask for a battery health test or commissioning capacity report, compare usable capacity rather than marketing capacity, confirm the inverter can perform the intended function, and verify surge protection based on voltage and location. It's a longer process than accepting the first proposal, but it avoids the expensive surprise of a battery system that looks good in the brochure and struggles in the field.