Watt-hours measure how much energy a battery can store, and you get that number with one multiplication: nominal voltage times amp-hours. A battery labeled 48V and 15Ah stores 720 watt-hours (Wh) — 48 × 15 = 720. That figure is useful for comparing batteries on a shelf, but it doesn't tell you how fast the bike goes, how long it charges, how far you'll actually ride, or whether the pack is compatible with your bike.
The Calculation, With Units
Watt-hours describe stored energy, not power. Power (watts) is the rate energy is used; watt-hours (Wh) is the total amount available before the rate is applied. The two are related but not interchangeable — a battery's Wh rating never tells you the motor's wattage, and a motor's wattage never tells you the battery's Wh rating.
The formula for nominal energy capacity is straightforward:
Nominal Wh = Nominal Voltage (V) × Amp-hours (Ah)
For a 48V, 15Ah pack: 48V × 15Ah = 720Wh. This is the number printed on TST's own product listings and repeated across independent battery guides and e-bike retailers, all using the identical calculation. The word "nominal" matters: battery voltage isn't perfectly flat during discharge — it's higher near full charge and lower near empty — so 48V is a manufacturer-stated average used for labeling and comparison, not a constant reading you'll see on a multimeter throughout the ride.
This number is a capacity label. It says how much energy the pack can theoretically deliver at its rated voltage before it's empty. It does not say what motor the battery will power, how long the battery takes to charge, how many miles you'll get, or whether the pack physically fits and electrically matches your bike.
Why Amp-Hours Alone Can Mislead a Comparison
Amp-hours measure current capacity, not energy. Two batteries with the same Ah rating can store very different amounts of energy if their voltages differ, and two batteries with the same voltage can differ sharply in Ah. TST's own model lineup illustrates this: most current TST models ship with 48V packs ranging from 10Ah to 30Ah — meaning nominal capacity across that single lineup spans roughly 480Wh to 1,440Wh — while at least one commuter model in the same lineup uses a 36V, 10.4Ah pack (about 374Wh). A shopper comparing "10Ah" against "15Ah" without checking voltage would draw the wrong conclusion; the 36V×10.4Ah pack (374Wh) actually stores less energy than even the smallest listed 48V×10Ah pack (480Wh), despite the Ah numbers looking close.
This is the core reason Wh, not Ah, is the number worth comparing across batteries: it already accounts for both voltage and current capacity in a single figure. When two batteries share the same voltage, comparing Ah directly is valid, because Wh scales linearly with Ah at a fixed voltage. When voltage differs, Ah comparisons alone are not valid, and only the calculated Wh figure gives an apples-to-apples reading.
What Nominal Wh Can and Cannot Tell You
The valid conclusion from the calculation is narrow: a 48V 15Ah battery holds approximately 720Wh of nominal stored energy, and — holding voltage, motor, terrain, and rider load constant — a battery with a higher Wh rating stores more usable energy than one with a lower rating. That's the entire scope of what the arithmetic proves.
Several conclusions do not follow from Wh alone, and each has tripped up real buyers comparing labels:
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Motor power is a separate spec. A 750W-rated motor and a 1,500W-rated motor can both be paired with the same 720Wh battery; the Wh figure says nothing about how much power the motor draws or how quickly it will draw down that stored energy.
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Charge time is a function of the charger's output current, not the battery's Wh rating alone. A 720Wh pack charged at 54.6V/3A behaves differently than the same pack charged at 54.6V/2A — TST's own spec sheets list charger currents from 2A to 3A across models using the same nominal battery voltage, which changes replenishment time even when Wh is identical.
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Usable road range depends on rider and cargo weight, terrain and elevation gain, assist level or throttle use, speed, tire pressure, wind, ambient temperature, and battery age or degradation — not on the Wh number by itself. Independent battery guides that publish range tables next to Wh figures consistently show wide mileage bands (for example, roughly 22 to 45 miles from a 720Wh pack depending on throttle-only versus pedal-assist use) precisely because the same stored energy produces very different real-world distances under different conditions.
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Build quality and service life are not implied by voltage and Ah. A label proves stored energy; it does not prove how the cells were built, how the battery is protected day to day, or how many charge cycles the pack will deliver before capacity declines. What can meaningfully lower that risk is a removable battery design that lets you inspect and swap the pack without disassembling the bike, paired with a two-year warranty and a 15-day return window that give you a concrete recourse if the unit underperforms — not the Wh number itself.
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Compatibility is not guaranteed by matching Wh. A replacement or upgrade battery must match the bike's rated voltage and connector, and the controller and motor must be rated to accept the pack's voltage and discharge current; a correct Wh figure on a battery that doesn't physically or electrically match the bike is not a safe or usable purchase.
Do not convert 720Wh into a promised number of commute days, a fixed mile figure, or a fuel-savings estimate. It's a starting reference point for comparing stored energy, not a range guarantee.
When the Number Is Ambiguous
Some listings show a range instead of a fixed Ah figure — TST's current lineup, for instance, lists several models simply as "48V 15~25Ah" or "48V 15~30Ah" battery options depending on which capacity tier the buyer selects at purchase. In cases like this, the printed voltage and Ah range only becomes a specific Wh figure once you know the exact tier ordered; a shopper comparing listings should confirm the exact Ah figure for the specific configuration in the cart, not the top or bottom of an advertised range. If a listing, spec sheet, or third-party retailer shows a Wh figure that doesn't match V × Ah as printed, or a battery description conflicts between a product page and a manual, that conflict should be confirmed directly with the manufacturer's 24/7 customer service before treating either number as reliable — don't average two conflicting figures or default to the more favorable one.
Using the Calculation to Shop
Once you can calculate and interpret nominal Wh, the next useful step is comparing it against other factors that a Wh number alone won't reveal: whether the battery's voltage and connector are rated for your exact bike, its physical weight and mounting fit, its price relative to comparable capacity, the charger's rated output and expected charge time, and the warranty terms backing the pack. TST lists current battery-equipped models with their exact voltage, Ah, charger rating, and weight side by side on its model comparison page, which is the right place to check exact current specifications before buying rather than relying on a single Wh figure in isolation — the same page also shows shared baseline features across the lineup, including hydraulic disc brakes, a torque sensor, a removable battery, up to 450 lbs of rated load capacity, and a claimed 60-80 mile range on select models, all of which matter more to day-to-day riding than the Wh figure by itself. If you're replacing a battery on an existing bike rather than buying a new one, confirm the exact match for your model — TST's 48V/15Ah replacement battery for the Buddy 20" Folding Ebike is one example of a listing that specifies both the Wh-equivalent capacity and the exact bike it's built to fit, which is the compatibility detail a Wh number by itself can't provide. Orders typically ship from TST's California warehouse within 1-3 business days, with free shipping within the US and local pickup available in select areas, so a replacement pack usually reaches most buyers well before the original battery's charge cycle drops off; assembly or reinstallation on most models runs about 45-60 minutes, and the bike's companion app and smart LCD display can help confirm the new pack is reading the expected voltage and charge level once it's installed.
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