Tesla Battery Health, Model S Replacement Cost, Solar Scale & Level 2 Charging: A Business Buyer's Field Notes

I'm not an engineer. I'm the office administrator for a 180-person manufacturer, and most of what I buy has to be approved by operations and finance. I took over purchasing in 2020, and by early 2024 I'd become the company's reluctant Tesla battery person: our fleet included a 2015 Model S 85 and a Model Y Long Range. In the same quarter, three questions landed on my desk: how to check Tesla battery health in the old S, what a Tesla Model S battery replacement cost would be, and whether solar plus EV charging for our two buildings was worth it.

Every article I found gave one universal answer. There isn't one. The right answer depends on the problem you're solving, so I'll write this the way I needed it: as a decision tree, not a formula.

How to Check Tesla Battery Health (And Why You're Checking Changes the Answer)

The fastest no-cost check is to charge to 100 percent once and compare the displayed rated range to the car's original EPA range. For a 2015 Tesla Model S 85, the original EPA number was 265 miles. Ours showed 228 miles at a full charge, which is about 14 percent lower than new. For a 10-year-old EV, that is not alarming. But it's only a starting point.

1. You're curious or deciding whether the car still fits your daily use. Stop after the full charge test. Compare the number to your actual routes, not to the day you bought the car. A loss under 15 percent rarely changes the decision when the car only does 40 miles per day.
2. You're buying or selling a used Tesla. Don't rely on a screenshot of the range display. Ask the seller to run a battery health check at Tesla service, or pull data through a third-party tracking tool, and get the estimated capacity in kWh. The display is a range estimate, not a measured capacity. A few percent of degradation can move a used-car price by thousands of dollars.
3. You're planning a fleet. Ignore the percentage for a minute. Ask whether the usable kWh still covers the route in January with the heater running. When Tesla service ran a battery health check on our S, the report gave us a capacity number we could file with finance. The range display moved around too much to trust on its own.

Tesla Model S Battery Replacement Cost: Our Quote and the Three Situations That Matter

I called Tesla service in October 2024 and asked directly. The quote for a remanufactured pack for our 2015 Model S 85 was $24,800 before tax. With 6 percent Michigan sales tax, it came to about $26,300. That included parts, labor, and the core exchange; it did not include towing. That's our quote on our car, not a universal price. Tesla Model S battery replacement cost varies a lot by year, pack size, and whether you're getting a remanufactured unit or a newer chemistry.

After getting that number, I split the decision into three scenarios:

1. The battery is degraded but still covers your routes. Wait. There is no maintenance rule that says you replace at 15 percent loss. Our S still shows roughly 220 miles at a full charge, and the daily route is 40 miles. A new pack would add range, but it would not change how we use the car.
2. The battery has died or collapsed. Compare the battery quote with the cost of replacing the vehicle as a whole, not with the car's trade-in value. A $26,000 battery in a $12,000 car is not automatically a mistake if it means avoiding a $35,000 replacement vehicle. If the chassis is solid and you plan to keep it for years, the replacement can make sense. If you were already thinking about another EV, do that instead.
3. You plan to sell within three years. Don't put a new battery in a car you're about to sell. You won't recover the premium at resale. Disclose the real battery numbers to the buyer and let the market price it accordingly.

This is where the transparency lesson hit me. Some of the other quotes we received were cheaper at the top line, but I had to ask each vendor, what's not included? Towing, removal labor, warranty location, core logistics, taxes. Tesla's quote was the clearest for our comptroller to evaluate. When you are spending $26,000, clarity has a real value.

Scale of Solar System: Size It From the Bill, Not a Sales Pitch

We asked solar vendors for proposals and got three different answers: 97 kW, 154 kW, and 240 kW. None was right, because we let the vendors choose the objective. You have to choose the objective first.

• You want to lower the utility bill. Size the system to the consumption you can actually use or export under your utility's rules.
• You want to stay running during an outage. From the outside, it looks like adding more panels is enough. The reality is that most solar systems shut down when the grid goes down. Resilience requires a battery and a transfer switch, not just a bigger array.
• You want to power EV charging with solar. A lot of charging happens overnight, so the solar output needs to flow through battery storage. That changes both the scale and the cost.

Once we picked the objective, the sizing formula was simple:

Annual kWh you want to offset ÷ (annual sun hours × 0.75).

We wanted to offset about 120,000 kWh of our 460,000 kWh annual usage. In Michigan, we get roughly 1,400 usable sun hours per year, sometimes fewer in a bad winter. The math came out to about 115 kW of DC solar.

For space planning, a 115 kW system uses around 285 modern 400-watt panels. With racking and service aisles, each panel takes up about 25 square feet, so we needed roughly 7,000 to 8,000 square feet of roof. Our plant roof had enough. If you don't have the roof area, the available footprint sets the scale before the spreadsheet does.

What the Solar Inverter FPGA Conversation Actually Means

The term solar inverter FPGA came up when our engineering consultant reviewed the proposals. FPGA stands for field-programmable gate array, and in a solar inverter it's used for fast, real-time control of power conversion and grid protection. Inverters are basically small computers with power electronics bolted on. They need to react to grid disturbances in microseconds, not milliseconds.

For a business buyer, the FPGA detail matters less than these questions: Is the inverter model named in the contract? Does the warranty run 10 to 15 years? Can the manufacturer actually service the unit in your region? The cheapest solar proposal we received didn't list an inverter model at all. The adders showed up later, after we asked for the full contract. The 20 percent savings evaporated once the engineering stamps and utility upgrades were included.

How Many kWh Does a Level 2 Charger Use?

If you searched for how many kwh does a level 2 charger use, the direct answer is that it depends on the circuit. A Level 2 charger pulls 240 volts, and the current is set by the circuit ampacity. Most commercial installs run from 16 amps to 48 amps of continuous current.

So a charger on a 60 A circuit will use about 11.5 kWh per hour of active charging at the wall. The car's battery stores slightly less than that after conversion losses, usually 10.5 to 11 kWh per hour. On a typical Tesla, that adds roughly 35 to 40 miles of range per hour.

The more useful number for a business is total daily energy, not the per-hour peak:

• Employee charging: A typical EV commute of 30 to 40 miles needs about 10 kWh. One 7.7 kW charger can cover that in about an hour and a half.
• Fleet charging with a fixed departure time: The charging window matters more than the charger's peak rate. If eight vehicles need 320 miles of range per day, that's roughly 90 kWh to replace. Spread across an 8-hour overnight window, the average load is about 11 kW, but you still need enough connectors so each vehicle gets plugged in.
• Existing building demand: Six chargers at 7.7 kW can add a 46 kW peak to a building that never saw that load before. If your utility charges for demand, unmanaged charging can make your electric bill jump by more than the charging itself costs.

For our building, we approved four Tesla Wall Connectors on 60 A circuits. That gives us flexibility for employee cars and for future fleet vehicles without committing to a huge infrastructure build on day one.

Which Scenario Are You In? A 10-Minute Decision Guide

1. For battery health: If a financial decision or a sale depends on the number, pay for a real battery health check. Otherwise, do the full charge test and move on.
2. For battery replacement: Ask how many more years you will keep the vehicle and what the alternative vehicle actually costs. Don't compare the battery quote to the car's resale value alone.
3. For solar: Write down the problem first. If you need outage resilience, you need storage. If you need a lower bill, you need panels sized to your consumption. If you want to charge EVs with solar, the battery changes the design.
4. For Level 2 charging: Start with your fleet's daily kWh need, then check the building's spare electrical capacity, then pick the charger amperage. That order rarely fails.

In the end, we kept the original battery in the Model S, approved the 115 kW rooftop solar system, and signed off on the four Wall Connectors. We skipped the stationary battery for now because our current utility tariff doesn't justify it. That's the unglamorous truth: the spreadsheet made the decision, not the marketing.

What made the whole process easier was a vendor that itemized everything up front. I've learned to ask what's not included before I ask what's the price. In energy purchasing, the cheapest first number is rarely the cheapest final number. The quote that lists its fees clearly is the one you can actually take to finance.