What a mechanic actually checks first
Range complaints get diagnosed backward from what most people expect: the bike first, the battery last. The opening minutes of a house call are mechanical. Both wheels get lifted and spun to feel for brake drag, the tires get gauged against their sidewall rating, and the drivetrain gets a listen, because on a heavy bike those problems imitate a dying pack convincingly.
Then the charge cycle gets verified end to end: we confirm the charger actually finishes, holding the pack until the light goes green, and check what voltage the pack settles at afterward. A charger that quits early, or a pack that never reaches full voltage, gives up range on every single charge without a single cell being bad.
Last comes the measurement that settles everything: a load test. The tech puts the battery under a controlled draw and watches how far the voltage sags and how quickly it recovers. A healthy pack holds its voltage under load. An aged pack, or one with a weak cell group, dips hard and trips its low-voltage cutoff long before the capacity gauge says it should. That sag behavior, not the percentage on the display, is the pack's real report card.
We also ask about the boring variables before condemning anything: colder weather since the range was last normal, new routes with more climbing, heavier cargo, or a rack and panniers that arrived around the same time as the complaint.
DIY or call a tech
The tire and brake checks in the section above are the genuine owner-level path, and here is how to make them conclusive: after airing the tires and confirming the wheels spin free, ride a familiar loop the bike used to handle easily, starting from a full charge in mild weather. If the range comes back, the case is closed and it cost nothing. If the loss arrived with the first cold snap, park the judgment until it warms up, since lithium capacity dips in the cold and returns on its own.
The tech line is the load test. It takes equipment and interpretation, and it is the difference between replacing a pack on a hunch and replacing it on evidence. Sourcing is tech territory too: a replacement has to match voltage, connector, and mounting, and our recommendation is to insist on a UL-certified pack and skip the bargain listings, because the savings are not worth what a badly built pack can do in a garage.
The standing battery-safety notes, as our recommendation: never open a lithium pack to replace cells yourself, charge on a hard surface where you can see the pack, unplug at green, and bring the battery indoors rather than leaving it on the bike through freezing nights.
What the repair costs and why
Our network's typical range for this symptom is $90 to $800, and the two ends are entirely different repairs. The $90 end is the outcome we root for: a load test that clears the pack, paired with the service work that was quietly eating the range. The $800 end is a pack that failed its test and needs replacement, with the exact figure driven by brand and availability. Brand matters enough that the table below deserves a read: Rad's 48V packs, for example, are common and well understood, so a tested verdict and a replacement path land between $90 and $650.