A Used EV Buying Example: From Seller Evidence to a Charging Budget

The car, the journey and the evidence

Imagine a used EV advertised with a 60 kWh original usable battery. You drive 12,000 km a year and sometimes make a 180 km round trip. The seller supplies a recent report showing 90% BMS state of health, plus a full-charge range estimate of 320 km and consumption of 16.5 kWh/100 km from comparable driving. You have access to a 7.4 kW home charger.

This is an original worked scenario, not a car we inspected or a set of market averages. Its purpose is to show how a decision changes when the evidence changes. A good starting record distinguishes a manufacturer specification, a seller’s report and your own planning assumption. Those categories should stay visible through the calculation.

1. Cross-check the capacity without blending the results

Multiply 320 by 16.5 and divide by 100: the range-based inference is 52.8 kWh, or 88% of the original usable baseline. The report’s 90% would correspond to 54 kWh if its method uses that same 60 kWh reference. The difference is 1.2 kWh, or two percentage points of the original capacity.

Do not average 88% and 90% into a supposedly verified 89%. They describe different methods. First check whether the range was predicted from the same driving conditions as the consumption, whether the report covers the installed pack and whether both references are usable capacity. With the health estimator’s selected ±10% sensitivity, the inferred capacity spans 47.5–58.1 kWh. That broad interval shows how much the inputs matter; it is not the accuracy rating of a diagnostic test.

In the Used EV Analyzer, enter capacity 60, range 320, consumption 16.5 and uncertainty 10. Enter 90 separately as reported BMS SoH. Only mark a supporting report as available when you actually have it.

2. Match the charge window to the trip

The analyzer’s range illustration uses the inferred 52.8 kWh from full charge down to a 10% reserve. At 16.5 kWh/100 km, that gives 288 km. It does not describe a journey that begins at 80%.

For that journey, use the separate Range Calculator with capacity 52.8, start 80, reserve 10, consumption 16.5 and additional consumption increase 0. The planning window contains 36.96 kWh and gives 224 km. If consumption rises to 21 kWh/100 km, the same charge window gives 176 km: less than the proposed 180 km trip. That is a reason to change the departure charge or charging plan, even though the car’s headline full-charge range looked sufficient.

Avoid adding a second winter penalty when the higher consumption already represents winter driving. The tool is useful because the reserve and consumption changes are explicit, allowing you to identify what makes the trip feasible.

3. Turn the driving pattern into a budget

At 12,000 km a year and 16.5 kWh/100 km, the car uses 1,980 kWh at the battery. With 10% of grid energy lost during charging, the billed energy is 1,980 ÷ 0.90 = 2,200 kWh. At the illustrative home rate of £0.25/kWh, that is £550 a year, or £45.83 per average month.

If 30% of billed energy instead comes from public charging at £0.65/kWh, the weighted energy price becomes £0.37/kWh. The annual amount rises to £814, or £67.83 per month. This comparison assumes the same loss rate for each location; change it if your evidence supports different rates. Subscription, parking and connection fees must be added separately.

The analyzer’s single tariff field can represent that weighted rate, but it does not calculate the mix for you. The Charging Tariff Comparison tool has separate home and public shares. Neither figure includes insurance, tax, repairs, finance or depreciation.

4. Check whether charging fits your evening

The analyzer’s AC illustration uses the entered original capacity over a 20–80% window: 60 × 0.60 = 36 kWh. With a 7.4 kW supply, an 11 kW vehicle limit and the same 10% loss assumption, it takes about 5 hours 25 minutes. This is a baseline charging scenario, not a measurement of how much the aged battery accepts.

Use the Charging Time Calculator if you want to test current usable capacity instead. Entering 52.8 kWh gives 31.68 kWh for that charge window and about 4 hours 46 minutes at 7.4 kW. Actual power sharing, heating and vehicle behaviour may lengthen the session. A larger advertised charger rating does not help if the car or your supply cannot accept it.

5. Finish with the unresolved evidence

Leave warranty dates and distance limits blank until the seller supplies the applicable documents. A current manufacturer webpage is a starting point; it cannot establish the contract for an older import or repaired battery. Similarly, an asking price does not tell the analyzer whether the car is good value because it has no live valuation database.

This example produces three practical requests: clarify the report’s reference capacity, check a representative higher-consumption journey and obtain the warranty and charging records. It does not produce a buy-or-avoid verdict. Keep the numerical scenarios alongside the inspection findings and compare another candidate using the same route, energy prices and ownership period.