How to calculate battery Ah?

Reading: it's on the battery label. Sizing: Ah = (load × hours) / (DoD × Peukert × inverter eff). Use the calculator above in Sizing mode.

How to calculate battery a h?

Same answer — "how to calculate battery a h" and "how to calculate battery ah" are the same query. Ah = (load_amps × runtime_hours) / DoD; with Peukert correction for lead-acid (multiply by Peukert factor 0.7–0.9 at high C-rate).

How to calculate battery ampere hour?

How to calculate battery ampere hour: ampere-hour = current × time. From a battery label, the rated Ah is given at a specified discharge rate (typically C/20 for lead-acid). To size the required ampere-hour for a load: Ah = (I_load × t_required) / DoD.

How to calculate battery watt hours?

How to calculate battery watt hours: Wh = Ah × V. A 100 Ah, 12 V battery stores 1 200 Wh = 1.2 kWh. Usable Wh = total × DoD. For LFP at 80 % DoD: 1 200 × 0.8 = 960 Wh.

How do you calculate battery watt hours?

Same formula — how do you calculate battery watt hours uses Wh = Ah × V, then multiply by DoD for usable energy and by the inverter efficiency (typically 0.92–0.96) for AC loads. The Energy mode in the calculator above shows both total and usable Wh.

How do you calculate battery watt-hours?

Wh = Ah × V. A 100 Ah, 12 V battery stores 1200 Wh = 1.2 kWh. Usable Wh = total × DoD. The Energy mode in the calculator above shows both.

How to calculate battery amp hours?

Same as Ah. Amp hours = ampere-hours = Ah. From label: read directly. From load: Ah = I × t / DoD. The calculator handles both directions.

How to calculate the battery life?

Same procedure as above — runtime t = (Ah × DoD) / I_load with Peukert correction for lead-acid; cycle life from manufacturer DoD curve divided by daily cycle count. The "the" wording is just a phrasing variation.

How to calculate a battery life?

Pick chemistry, read Ah and DoD limit, divide by load current. Same answer as "how to calculate battery life" or "how to calculate the battery life" — all three phrasings reduce to the same formula.

How to calculate battery capacity?

Battery capacity is rated in ampere-hours (Ah). To compute required capacity from a load: Ah = (I_load × runtime_hours) / DoD. The full battery capacity calculation workflow is on the dedicated capacity sizing page; for the underlying physics see battery capacity reference.

How to calculate the battery capacity?

Same as above — "how to calculate the battery capacity" is the same query with an extra article. Ah = (I × t) / DoD; multiply by V to get Wh; add 20–25 % safety margin for ageing.

How to calculate battery run time?

Battery run time = (Ah × DoD) / I_load (linear); multiply by Peukert factor for lead-acid at high C-rate. The calculator above does this in Runtime mode.

How to calculate calculate battery size / calculate battery duration?

The "calculate battery size" and "calculate battery duration" workflows are the inverses of one another: given runtime → size (Ah), or given Ah → runtime. Both are in the Sizing and Runtime modes of the calculator above respectively.

Why is actual runtime shorter than calculated?

Three reasons: (1) Peukert effect — lead-acid loses 20–30% effective capacity at high discharge rates. (2) Temperature — cold reduces capacity ~1% per °C below 25°C. (3) Ageing — battery loses 20% capacity over its rated life. (4) Inverter efficiency — typically 5–10% loss on AC loads. Always derate the calculated runtime by 15–20% for real-world conditions.

How long does a 100 Ah battery last?

Depends on load. At 12 V (1200 Wh total): 100 W load → ~10 hours at 100% DoD, ~5 h at 50%. 500 W load → ~2 hr. At 24 V (2400 Wh): twice the runtime for the same load. Use the calculator with your specific load and chemistry for an accurate answer.

Tutorial + Tool · Battery runtime · Solar / UPS / RV / EV

Calculate battery life

Step-by-step procedure for computing how long a battery will last under a known load. Worked Ah / Wh examples, charge-time formula, Peukert correction. Calculator opens in Runtime mode. Reviewed by a licensed PE.

Use the battery life calculator

The Runtime tab is selected. Enter your battery capacity, voltage, DoD, and load — the calculator returns hours of runtime with proper Peukert correction.

CALC.008 Battery · Runtime + Sizing + Energy · 6 chemistries · Peukert

Chemistry[Chem]

Battery voltage[V]

Depth of discharge[DoD]

Runtime

— h

—

Linear runtime (no Peukert): —
Peukert-corrected runtime: —
Usable energy at DoD: — Wh
Total stored energy: — Wh
C-rate (load / capacity): —
Estimated cycles to 80%: —
Estimated weight: — kg
Standard 100 Ah modules: —

FORMULA · t = (C × DoD) / I × Peukert SOURCE · IEEE 485 · IEC 60896 · PEUKERT 1897

Battery life — at a glance

Battery life formula: runtime (h) = (Ah × DoD) / I_load. For lead-acid at high discharge, multiply by Peukert factor (0.7–0.9 reduction).
Ah from a load: Ah = (load_amps × runtime_hours) / DoD, then add 20–25% safety margin for ageing.
Wh from Ah: Wh = Ah × V. A 100 Ah / 12 V battery stores 1 200 Wh; usable Wh = total × DoD × inverter efficiency.
Charge time formula: charge time (h) ≈ Ah / I_charge × 1.1–1.2 (efficiency loss). A 100 Ah battery at 10 A charge: ~11–12 hours from empty.
Peukert correction: For lead-acid at high C-rate: t_real = t_linear × (I_ref / I)^(k−1), with k ≈ 1.15–1.30. Lithium k ≈ 1.05 (negligible).
AC load through inverter: DC current = P_AC / (V × η_inv), where η_inv ≈ 0.92–0.96. A 200 W AC load at 12 V = ~17.5 A DC.
Effective capacity vs DoD: Usable Ah = rated × DoD. Lead-flooded 50%, AGM 80%, LFP 80–100%. Cycling deeper than the limit cuts cycle life sharply.

The battery life formula

Eq. 01 — Runtime hours SI · Peukert + Ohm

t = \frac{C \cdot \mathrm{DoD}}{I} \cdot \left(\frac{I_{ref}}{I}\right)^{k-1}

t: runtime, h
C: rated capacity, Ah
DoD: depth-of-discharge fraction, —
I: load current, A
I_ref: rated current (C/20 typical), A
k: Peukert exponent (1.05–1.30), —

Worked example: 100 Ah AGM at 200 W AC load

Step	Calculation	Result
DC current at 12 V (with inverter)	200 / (12 × 0.95)	17.5 A
Linear runtime at 80% DoD	(100 × 0.80) / 17.5	4.6 h
Peukert correction (k = 1.10)	(5 / 17.5)^0.10	0.882
Real runtime	4.6 × 0.882	4.0 h
If LFP instead (k = 1.05)	4.6 × 0.94	4.3 h

How to calculate battery life, step by step

Read the battery's rated capacity in Ah. On the label. Note the rate ("100 Ah at 20-hr rate"). Lower rates → fewer Ah, higher rates → also fewer Ah due to Peukert.
Apply the DoD limit. Lead-acid: 50% max for cycle life. AGM/Gel: 80%. LFP: 80–100%. Usable Ah = rated × DoD.
Find the load current. For DC load: I = P/V (or directly given in A). For AC load through inverter: I = P / (V × η_inv), where η_inv is typically 0.95.
Compute linear runtime. t_linear = (Ah × DoD) / I. This is the simple, ignoring-Peukert estimate.
Apply Peukert correction (lead-acid only). t_peukert = t_linear × (I_ref / I)^(k-1), where I_ref = C/20 and k = 1.15–1.30 for lead. Lithium k ≈ 1.05 — correction is small.
Convert to days. If load runs only N hours per day: days_of_runtime = t_peukert / N. Useful for backup / off-grid sizing.

Related concepts on this site

Frequently asked questions

How to calculate battery Ah?: Reading: it's on the battery label. Sizing: Ah = (load × hours) / (DoD × Peukert × inverter eff). Use the calculator above in Sizing mode.
How to calculate battery a h?: Same answer — "how to calculate battery a h" and "how to calculate battery ah" are the same query. Ah = (load_amps × runtime_hours) / DoD; with Peukert correction for lead-acid (multiply by Peukert factor 0.7–0.9 at high C-rate).
How to calculate battery ampere hour?: How to calculate battery ampere hour: ampere-hour = current × time. From a battery label, the rated Ah is given at a specified discharge rate (typically C/20 for lead-acid). To size the required ampere-hour for a load: Ah = (I_load × t_required) / DoD.
How to calculate battery watt hours?: How to calculate battery watt hours: Wh = Ah × V. A 100 Ah, 12 V battery stores 1 200 Wh = 1.2 kWh. Usable Wh = total × DoD. For LFP at 80 % DoD: 1 200 × 0.8 = 960 Wh.
How do you calculate battery watt hours?: Same formula — how do you calculate battery watt hours uses Wh = Ah × V, then multiply by DoD for usable energy and by the inverter efficiency (typically 0.92–0.96) for AC loads. The Energy mode in the calculator above shows both total and usable Wh.
How do you calculate battery watt-hours?: Wh = Ah × V. A 100 Ah, 12 V battery stores 1200 Wh = 1.2 kWh. Usable Wh = total × DoD. The Energy mode in the calculator above shows both.
How to calculate battery amp hours?: Same as Ah. Amp hours = ampere-hours = Ah. From label: read directly. From load: Ah = I × t / DoD. The calculator handles both directions.
How to calculate battery life?: Single discharge runtime: t = (Ah × DoD) / I, with Peukert correction for lead-acid. Cycle life (years): rated cycles × DoD-curve adjustment, divided by cycles per year. Lead at 50% DoD daily: ~3 yr. LFP at 80% DoD daily: ~8 yr. The runtime calc above shows hours; cycle life is shown in the detail panel.
How to calculate the battery life?: Same procedure as above — runtime t = (Ah × DoD) / I_load with Peukert correction for lead-acid; cycle life from manufacturer DoD curve divided by daily cycle count. The "the" wording is just a phrasing variation.
How to calculate a battery life?: Pick chemistry, read Ah and DoD limit, divide by load current. Same answer as "how to calculate battery life" or "how to calculate the battery life" — all three phrasings reduce to the same formula.
How to calculate battery capacity?: Battery capacity is rated in ampere-hours (Ah). To compute required capacity from a load: Ah = (I_load × runtime_hours) / DoD. The full battery capacity calculation workflow is on the dedicated capacity sizing page; for the underlying physics see battery capacity reference.
How to calculate the battery capacity?: Same as above — "how to calculate the battery capacity" is the same query with an extra article. Ah = (I × t) / DoD; multiply by V to get Wh; add 20–25 % safety margin for ageing.
How to calculate battery run time?: Battery run time = (Ah × DoD) / I_load (linear); multiply by Peukert factor for lead-acid at high C-rate. The calculator above does this in Runtime mode.
How to calculate calculate battery size / calculate battery duration?: The "calculate battery size" and "calculate battery duration" workflows are the inverses of one another: given runtime → size (Ah), or given Ah → runtime. Both are in the Sizing and Runtime modes of the calculator above respectively.
Why is actual runtime shorter than calculated?: Three reasons: (1) Peukert effect — lead-acid loses 20–30% effective capacity at high discharge rates. (2) Temperature — cold reduces capacity ~1% per °C below 25°C. (3) Ageing — battery loses 20% capacity over its rated life. (4) Inverter efficiency — typically 5–10% loss on AC loads. Always derate the calculated runtime by 15–20% for real-world conditions.
How long does a 100 Ah battery last?: Depends on load. At 12 V (1200 Wh total): 100 W load → ~10 hours at 100% DoD, ~5 h at 50%. 500 W load → ~2 hr. At 24 V (2400 Wh): twice the runtime for the same load. Use the calculator with your specific load and chemistry for an accurate answer.

Sources and methodology

Peukert, W. — original Peukert\'s law, 1897.
IEEE Std 485, 2020.
IEC 60896 — Stationary lead-acid batteries.