An informed buyer asks about SOH before asking about price. Battery state of health, expressed as a percentage of the original capacity still available, drives real range, resale value and the peace of mind of the next owner. A dealer who cannot answer loses credibility, and often the sale. In the fourth quarter of 2025, the average time to resell a used electric vehicle stood at 161 days across all ages, according to the quarterly barometer published by Mobilians and Avere-France. Five and a half months of capital tied up in a car whose most expensive component nobody can describe.

Used electric is a professional market

Professional networks handle 84 % of used electric vehicle transactions, against 76 % for used combustion vehicles (Mobilians and Avere-France, Q4 2025 barometer). That gap is not incidental. On electric, the private seller fades away, and the reason sits in the SOH question. A buyer with no warranty, no charging history, no diagnostic and no recourse does not take the risk. He goes to a professional.

Stock held by professionals reached 61,613 units in the fourth quarter of 2025, up 5 % over one quarter (Mobilians and Avere-France). Used electric vehicles accounted for 3.3 % of used cars registered in France in 2025, against 2.5 % in 2024 (SDES and NGC-Data figures reported by L’Argus). A small segment, growing fast, entirely in professional hands, where the seller with an answer starts several lengths ahead.

What SOH measures, and what it does not

State of health compares a battery’s current usable capacity to its original capacity. A battery at 90 % SOH delivers roughly nine tenths of the energy it stored when new. It is a wear indicator, not a clean bill of electronic health: it says nothing about the battery management system, the charging power accepted, or behaviour in deep cold.

What it does say is enough to frame a negotiation. Two identical cars, same model year, same mileage, do not hold the same value if their batteries have lived differently. SOH makes that difference visible, therefore discussable, therefore quantifiable. Without it, the buyer assumes the worst and the seller defends a price with no evidence.

161 days: the cost of a missing number

The average price of a used electric vehicle under three years old reached 32,261 euros in 2025, 16 % below the average new car price excluding purchase incentives, measured at 38,633 euros (Mobilians and Avere-France). Set against an average 161-day rotation, every week saved on reselling such a vehicle represents a meaningful share of the capital tied up in a forecourt. A dealer who ignores SOH does not lose a sale. He loses days, one at a time, on every enquiry that walks off to find elsewhere the answer nobody gave.

Waiting is getting more expensive. In the fourth quarter of 2025, the used electric market grew 23 % on the previous quarter, driven mainly by private buyers, with increasing use of leasing (Mobilians and Avere-France). Demand is arriving. The question is who will be ready to answer it.

Getting the SOH without taking the car off the forecourt

The professionals we meet all describe the same obstacle: getting that number means a trip to a franchised workshop, a paid diagnostic, and a delay. On a car that needs to move, that is three obstacles for one line in a listing.

This is why Osmosia built an SOH simulator, freely available at https://osmosia-simulateursoh.netlify.app/. It provides an estimate designed to frame a commercial conversation and to document a listing. An estimate is not a manufacturer diagnostic: where a transaction requires one, or in the event of a dispute, the official diagnostic remains the reference.

Answer the SOH question within the hour, not the next morning

The question lands in the listing inbox, often in the evening, often first. Auditing 2,241 US companies, Harvard Business Review measured an average response time of 42 hours and found that 23 % never replied at all; those answering within the hour were roughly 7 times more likely to hold a qualifying conversation (Oldroyd, McElheran, Elkington, 2011). On an electric vehicle the delay costs double: a buyer waiting for an SOH answer is a buyer already in doubt.

Osmosia answers messages received on listings in under fifteen minutes, seven days a week from 7am to 11pm, delivers the information requested, qualifies intent and books the appointment. On an electric forecourt, that means giving the right answer at the exact moment the buyer asks, rather than the following morning, once he has written to three other listings.