Battery charge time and electricity cost both start from the same idea — a device draws power over time — but they measure different sides of it. The battery charge time calculator asks how long a charge takes: it turns capacity and current into hours. The electricity cost calculator asks what running something costs: it turns watts and hours into kilowatt-hours and then dollars. Neither replaces the other; the battery page links to the electricity cost calculator for the cost side, and the electricity page treats chargers as ordinary appliance rows.
What each calculator does
The battery charge time calculator takes battery capacity in mAh, charger output current in amps, current and target charge percentages, and a charging method. Capacity converts to amp-hours (÷ 1000), the charge difference is (target − current) ÷ 100, and the estimate is (capacity in Ah × charge difference) ÷ (charger current in A × efficiency), displayed as whole hours and floored minutes. The target must be higher than the current level or the form returns an invalid state.
The electricity cost calculator takes a rate in dollars per kWh and a list of appliance rows, each with a name, watts, hours per day, and whole-number quantity. Each row converts to daily kWh: watts × hours × quantity ÷ 1000. The total multiplies by the rate for daily cost, by 30 for the monthly result, and by 365 for the yearly result, with a per-appliance monthly breakdown.
Side-by-side
| Battery charge time calculator | Electricity cost calculator | |
|---|---|---|
| Question answered | How long until this battery reaches the target charge? | How much does running these devices cost per day, month, and year? |
| Core formula | (Ah × charge fraction) ÷ (A × efficiency) | Σ (watts × hours × quantity ÷ 1000) × rate |
| Key inputs | mAh, charger amps, current %, target %, method | Rate per kWh; watts, hours, quantity per row |
| Efficiency | 90% standard, 85% fast, 70% wireless | Implicit in measured watts, not a separate factor |
| Output | Whole hours plus floored minutes | Dollars to two decimals, daily/monthly/yearly |
| Shared trait | Planning estimate with visible assumptions | Planning estimate with visible assumptions |
When to use which
Use the battery charge time calculator when the question is time: planning a phone top-up before leaving home, comparing a standard charger with a wireless pad, estimating a power-bank recharge, or checking whether a published charging claim is plausible. Use actual charger current when possible, calculate to 80% as well as 100% for trip planning, and remember the final part of a charge often slows as lithium-ion batteries taper.
Use the electricity cost calculator when the question is money: estimating what a refrigerator, LED lights, air conditioner, or charger adds to a bill, or sorting household loads by monthly cost to find the largest ones first. Lowering hours on a high-watt device is often more valuable than unplugging tiny chargers, and the page recommends measured or average watts over nameplate ratings for cycling and throttling loads.
Limits and disclaimer
Both pages describe their results as planning estimates with explicit assumptions. The battery estimate is not a battery-management model: it uses a simple average-current formula that may be most realistic for partial charges, and it should not be used to exceed manufacturer charging limits. The electricity result is the variable energy cost of the entered devices only — it uses a clean 30-day month, excludes fixed customer charges, and will not match a utility bill exactly. Both calculators validate inputs strictly: the battery form rejects a target below the current level, and the electricity form rejects missing or invalid rows rather than skipping them.