Two bikes with the same battery rating can return wildly different mileage on the same route, and the reason usually sits in the motor and where it applies its force rather than in the cells. A careful reader starts by separating the two claims a spec sheet makes: how the bike moves, and how long it keeps moving. The first is a question of drivetrain architecture, the second is arithmetic plus a set of assumptions that almost never get printed. Both are checkable before you hand over money, and both change what the bike costs to keep.
Where the motor sits changes what the hill feels like
A hub motor drives the wheel directly, through a fixed internal reduction if it is geared, and it cannot use your cassette. That means on a long climb the motor is stuck at whatever speed the hill allows, drifting away from its efficient rpm band, drawing more current and making more heat for less forward motion. A mid-drive turns the crank, so it passes through every gear you have, and dropping two cogs restores the motor to a comfortable cadence exactly as it restores yours. On flat ground the difference narrows to almost nothing. On a repeated six percent grade it is the whole story.
Traffic separates them differently. Stop-start riding is a series of accelerations from zero, which is where a geared hub's fixed reduction gives an immediate shove without asking you to think, and where cadence-sensor systems feel pleasantly indifferent to how hard you push. A torque-sensing mid-drive meters output against your own effort, so it pulls away smoothly and predictably, which matters more at an intersection than raw punch does. The trade is wear: a mid-drive routes its power through your chain and cassette, and those parts wear faster than they would on an unassisted bike. Chains checked and replaced on time keep the cassette alive, and that is a cheap habit to build.
Reading the watt-hour figure without being flattered by it
Watt-hours are the only battery number worth comparing, and you can compute them yourself: nominal voltage multiplied by amp-hours. A 36-volt pack rated at 14 amp-hours is about 504 watt-hours, and a 48-volt pack at 14 amp-hours is about 672, which is why voltage alone tells you nothing about capacity. What a careful reader checks next is the cell brand, the warranty term and whether it covers capacity loss or only outright failure, and whether replacement packs for that frame are sold separately at all. The Department of Energy is the federal body responsible for lithium battery research and standards work in the United States, and its interest in cycle life is the same as yours: capacity fades gradually, and a pack you can replace in year five is a bike you still own in year eight.
Then there is the consumption side, expressed in watt-hours per mile. Divide pack capacity by your real per-mile draw and you have range. Everything else is assumption.
Why the quoted range is a laboratory number
Manufacturer range figures are generally produced on flat ground, in mild weather, at the lowest assist setting, with a light rider, smooth tires and no cargo. Change any one of those and the number moves. Riders who log commutes with a display that reports watt-hours consumed tend to find a wide band rather than a single figure, with economical flat riding at the bottom and heavy assist on hills at several times that draw, which means the same 500-watt-hour pack can plausibly deliver a modest errand radius or a genuinely long day. Cold weather trims usable capacity temporarily. Headwinds behave exactly like a hill that never ends.
The practical check is to size the pack against your worst plausible day rather than your average one, then confirm the number in the first two weeks of ownership by logging watt-hours against actual miles on your actual route. That gives you a personal per-mile figure that no brochure can argue with, and it turns range from a marketing claim into a planning tool you can rely on for the life of the bike.
What the two choices actually cost to live with
Hub bikes are typically cheaper, simpler and easier to service at a general shop, with the caveat that a rear hub makes flat repair a heavier job. Mid-drives cost more up front and add drivetrain consumables, and they repay it on steep terrain, with load, and in efficiency per watt-hour carried. Pick on terrain first, then on how the assist feels at a standing start, because that is the sensation you will meet a hundred times a week.