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E-Bike Battery Decoder

An e-bike battery’s energy is its voltage times its amp-hours: a 48 V, 14 Ah pack holds 672 Wh. A 48 V pack is 13 cells in series — 54.6 V when full, around 39 V near empty at rest (EM3ev) — and a 2-amp charger fills it in about 7 to 8 hours. At 672 Wh it can’t fly: the FAA caps spare lithium batteries at 100 Wh, or 160 Wh with airline approval.

No sign-up · works on your phoneUpdated September 21, 20266 sources

From the battery label

Nominal voltage

CapacityAhAmp-hours, e.g. 14 Ah or 14000 mAh ÷ 1000.

Unit

AhWh

Voltage you measured (optional)VAt rest — off the charger and not riding for at least a few minutes. Under load it reads lower.

Charger output (optional)AOn the charger's label, e.g. “Output 54.6V ⎓ 2A” → 2.

What it means

Energy

672Wh

Cells in series

13S

48 V nominal

Full / empty

54.6V

≈ 39.0 V near empty

Empty to full

7 h 00 min–8 h 03 min

With a 2 A charger

20% to 80%

4 h 12 min–4 h 50 min

The everyday top-up

Can't fly: 672 Wh is over the FAA's 160 Wh ceiling

The FAA allows spare lithium-ion batteries up to 100 Wh in carry-on bags, and up to two of 101–160 Wh with the airline’s approval. Spares never go in checked bags.

How this was calculated

Energy48 V × 14.0 Ah672 Wh

Cells in series48 V ÷ 3.6 V nominal per cell13

Full charge13 × 4.20 V54.6 V

Near empty13 × 3.00 V39.0 V

Charge time14.0 Ah ÷ 2 A, +0–15% to top off7 h 00 min–8 h 03 min

Charge levels use EM3ev’s published scale — 4.20 V per cell full, about 3.00 V near empty, straight-line in between. Controllers and battery management systems cut off at different points, so “empty” varies.

Your pack’s voltage chart (at rest)

100%

54.6

80%

51.5

60%

48.4

40%

45.2

20%

42.1

39.0

Worked example

A 48 V 14 Ah battery that reads 46.8 V at rest

Energy: 48 × 14 = 672 Wh. Cells: 48 V is 13 lithium-ion cells in series, so full is 13 × 4.20 = 54.6 V and near-empty about 13 × 3.00 = 39.0 V.

Charge level: 46.8 ÷ 13 = 3.60 V per cell, halfway between 3.00 and 4.20 — about 50%. Charge time: 14 Ah ÷ 2 A = 7 hours from empty, a little longer to top off (7 h 00 min to 8 h 03 min); from 50% it’s about half that.

Reference

E-bike battery voltage and charging charts

Resting voltage — off the charger and not riding for a few minutes. Under load, voltage sags and reads lower.

E-bike battery voltage chart by state of charge for 36V, 48V and 52V packs
Charge	36 V (10S)	48 V (13S)	52 V (14S)	Per cell
100%	42.0 V	54.6 V	58.8 V	4.20 V
90%	40.8 V	53.0 V	57.1 V	4.08 V
80%	39.6 V	51.5 V	55.4 V	3.96 V
70%	38.4 V	49.9 V	53.8 V	3.84 V
60%	37.2 V	48.4 V	52.1 V	3.72 V
50%	36.0 V	46.8 V	50.4 V	3.60 V
40%	34.8 V	45.2 V	48.7 V	3.48 V
30%	33.6 V	43.7 V	47.0 V	3.36 V
20%	32.4 V	42.1 V	45.4 V	3.24 V
10%	31.2 V	40.6 V	43.7 V	3.12 V
0%	30.0 V	39.0 V	42.0 V	3.00 V

Charging time, empty to full

E-bike battery charging time by capacity and charger output
Battery	Wh	2 A	3 A	4 A	5 A
36 V 10 Ah	360	5 h 00 min–5 h 45 min	3 h 20 min–3 h 50 min	2 h 30 min–2 h 53 min	2 h 00 min–2 h 18 min
36 V 14 Ah	504	7 h 00 min–8 h 03 min	4 h 40 min–5 h 22 min	3 h 30 min–4 h 01 min	2 h 48 min–3 h 13 min
48 V 14 Ah	672	7 h 00 min–8 h 03 min	4 h 40 min–5 h 22 min	3 h 30 min–4 h 01 min	2 h 48 min–3 h 13 min
48 V 17.5 Ah	840	8 h 45 min–10 h 04 min	5 h 50 min–6 h 42 min	4 h 23 min–5 h 02 min	3 h 30 min–4 h 01 min
52 V 20 Ah	1040	10 h 00 min–11 h 30 min	6 h 40 min–7 h 40 min	5 h 00 min–5 h 45 min	4 h 00 min–4 h 36 min

Amp-hours ÷ charger amps, plus up to about 15% for the final top-off — consistent with EM3ev’s published examples (48 V 14 Ah: 7–8 hours at 2 A).

Care numbers from the makers

E-bike battery storage, temperature and lifespan guidance
	Guidance	Source
Storage charge	30–60%	Bosch
Storage temperature	About 20 °C (68 °F); never below −10 °C or above 60 °C	Bosch
Charging	Not below 0 °C (32 °F) — bring a cold battery indoors first	EM3ev
Lifespan	500–700 full charge cycles standard; makers quote up to 1,000	Diamant
Flying	Spares ≤ 100 Wh, or two of 101–160 Wh with airline approval; carry-on only	FAA

How to use it

In 4 steps

1Find the label on the battery: nominal voltage (like 48 V) and capacity in Ah or Wh.
2Pick the voltage and enter the capacity — the tool gives watt-hours, cell count and full and empty voltage.
3Optional: measure the battery at rest with a multimeter on the charge port and enter the reading for its charge level.
4Optional: enter the charger's output amps (on its label) for charging time.

What the numbers on the battery mean

Volts is the push; amp-hours is how long it can keep pushing; multiply them and you get watt-hours, the fuel-tank size that decides range. A 36 V 14 Ah pack and a 48 V 10.5 Ah pack both hold about 504 Wh. Nominal voltage is a middle figure: lithium-ion cells run from 4.20 V full to roughly 3.00 V near empty, so a “48 V” pack of 13 cells reads 54.6 V off the charger.

That’s why a voltmeter can estimate charge — at rest. Under load the voltage sags, and real discharge curves are flatter in the middle than the straight-line scale used here, so mid-range readings are the least precise. A proper capacity test measures what the pack actually delivers against its rated watt-hours, and balance checks show whether one group of cells is dragging the rest down.

Lithium packs age with both cycles and time. Storing them around half charge at room temperature, and never charging them below freezing, is what the makers ask for. And since January 1, 2026, a replacement battery sold in California has to be lab-tested and labeled — see the battery safety guide.

FAQ

Battery decoder: questions

How many watt-hours is my e-bike battery?

Multiply the nominal voltage by the amp-hours on the label: 36 V × 10 Ah = 360 Wh, 48 V × 14 Ah = 672 Wh, 52 V × 20 Ah = 1,040 Wh. The FAA uses the same formula.

What voltage is a fully charged 48V e-bike battery?

54.6 volts. A 48 V pack is 13 lithium-ion cells in series at 4.20 V each when full. EM3ev's chart puts 50% at about 46.8 V and near-empty around 39.0 V, measured at rest — cutoff points vary by controller.

Can you take an e-bike battery on a plane?

Almost never. The FAA limits spare lithium-ion batteries to 100 Wh in carry-on bags, or up to two batteries of 101–160 Wh with the airline's approval, and spares can't go in checked bags. E-bike batteries are typically several hundred watt-hours.

How long does an e-bike battery take to charge?

Roughly amp-hours divided by the charger's amps, plus a bit to top off. EM3ev's examples: a 36 V 10 Ah pack takes 4.5–5 hours on a 2 A charger and 2.5 on a 4 A; a 48 V 14 Ah pack takes 7–8 hours on 2 A and 3.5–4 on 4 A.

How long does an e-bike battery last?

Diamant puts 500–700 full charge cycles as standard — about three to five years for most riders — with makers quoting up to 1,000. Pinkbike reports Bosch's battery warranty as two years or 500 cycles. Heat, storing full and deep discharges shorten it.

How should I store an e-bike battery?

Bosch recommends 30–60% charge (two or three LEDs), somewhere dry around 20 °C (68 °F), and never below −10 °C or above 60 °C. Don't charge it below freezing — EM3ev warns of lithium plating — and let a cold battery warm up indoors first.

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Sources

Where these numbers come from

[1]EM3ev, “48V Battery Voltage Chart for eBikes” (updated Sep 1, 2026) (opens in a new tab)4.20 V per cell full, ≈3.00 V near empty; measure at rest; cutoffs vary.
[2]EM3ev, “Charging E Bike” (Jan 9, 2026) (opens in a new tab)Example charge times by capacity and charger; no charging below 0 °C.
[3]FAA PackSafe — Lithium batteries (updated Aug 11, 2026) (opens in a new tab)Wh = V × Ah; 100 Wh limit, up to two 101–160 Wh spares with airline approval; spares carry-on only.
[4]Bosch eBike Battery Guide (opens in a new tab)Store at 30–60%, around 20 °C, never below −10 °C or above 60 °C.
[5]Diamant, e-bike battery service life (opens in a new tab)500–700 charge cycles standard; makers quote up to 1,000.
[6]Pinkbike, “How to maximise the life of your e-bike battery” (opens in a new tab)Reports Bosch's battery warranty as 2 years or 500 cycles.

Last reviewed September 21, 2026. Spot something wrong? Text (949) 891-5278 and it gets fixed.

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