Battery Calculators
Calculate battery runtime, charge time, capacity, and more. Every calculator works for all major battery types — LiFePO4, lead-acid, AGM, and lithium-ion.
Most people land on this page with one of three questions in mind: how long will a battery actually run my load, how long will it take to recharge, and how big a bank do I need for the days I want to go without sun or shore power. The calculators here answer those head-on, with the chemistry-specific math that generic spreadsheets skip. LiFePO4 holds 80–90% of its rated capacity at high discharge rates; flooded lead-acid loses 30–50% under the same load. AGM sits in between. The tools below account for that — depth-of-discharge limits, Peukert effects, inverter losses, and real-world temperature behavior — so the numbers you walk away with match what you'll measure on a meter, not what a marketing spec sheet promises.
The audience is mixed: weekend RV owners sizing a single drop-in to keep a fridge cold, full-time van-lifers building 600Ah banks, sailors planning a multi-day passage, and DIY off-grid builders putting together prismatic-cell packs. Pick the calculator that matches the question you're asking — start with the battery runtime calculator if you know your load and want hours, the charge time calculator if you've got a charger and want to know when you'll be full, or the capacity calculator if you're sizing from scratch. The chemistry-specific runtime tools (LiFePO4, AGM, lead-acid) are the right pick when the brand or chemistry is already locked in. The voltage-percentage and reserve-capacity tools answer the gauge-and-state-of-charge questions that come up mid-trip — “is this 12.4V reading still safe to discharge?” or “what does an 80-minute reserve-capacity rating mean for my actual fridge load?” Every calculator runs in your browser instantly, with no account wall, and every page cites the formula and source it's built on so you can re-derive the answer yourself.
Battery Runtime Calculator
Calculate how long your battery will last under any load. Enter capacity, voltage, and wattage for an instant runtime estimate.
Propane Generator Run Time Calculator
Calculate how long a propane generator runs on a given tank size. Enter tank weight, load, and generator efficiency.
12V Battery Runtime Calculator
Calculate how long a 12 volt battery lasts under any load. Pre-tuned for 12V deep cycle, AGM, and LiFePO4 systems.
LiFePO4 Battery Runtime Calculator
Estimate LiFePO4 battery runtime with accurate DoD and efficiency defaults. Compare lithium iron phosphate vs lead-acid.
Portable Power Bank Runtime Calculator
Find how long your portable power bank charges your phone, tablet, or laptop. Enter mAh, voltage, and device wattage.
Battery Charge Time Calculator
Calculate how long it takes to charge any battery. Enter capacity, charge current, and DoD for accurate charge time.
Battery Charge and Discharge Calculator
Calculate both charge and discharge times for your battery in one place. Model a complete daily battery cycle.
Cold Cranking Amps (CCA) Calculator
Calculate CCA requirements for your vehicle based on engine size, type, and climate. Find the right starting battery.
Battery Size for Inverter Calculator
Find the right battery capacity for your inverter. Enter load, runtime, and voltage for a proper battery sizing estimate.
How Long Will a 12V Battery Run a Refrigerator?
Calculate how long a 12V battery powers your refrigerator. Works for power outages, camping, and off-grid setups.
Deep Cycle Battery Runtime Calculator
Estimate deep cycle battery runtime for marine, RV, and off-grid use. Accounts for depth of discharge and Peukert losses.
Battery Capacity (Amp Hours) Calculator
Calculate battery capacity in amp-hours from watt-hours and voltage. Convert between Wh, Ah, and watts easily.
UPS Battery Backup Time Calculator
Calculate how long your UPS keeps devices running during an outage. Enter VA rating, load, and battery capacity.
Laptop Battery Runtime Calculator
Estimate your laptop battery life based on battery Wh rating and actual power consumption by usage mode.
RV Battery Runtime Calculator
Calculate how long your RV battery bank powers your camper. Enter your loads, battery size, and get real runtime.
Marine Battery Runtime Calculator
Estimate trolling motor and boat electronics runtime from your marine battery. Built for anglers and boaters.
Car Battery Runtime Calculator
Calculate how long a car battery powers accessories with the engine off. Know the limits before you drain your starter.
Reserve Capacity to Amp Hours
Convert battery reserve capacity (RC minutes) to amp-hours. Understand what RC means and how it compares to Ah.
Watt Hours to Amp Hours Calculator
Convert watt-hours to amp-hours at any voltage. Essential for comparing batteries rated in different units.
Battery Voltage to Percentage Calculator
Convert battery resting voltage to state of charge percentage. Charts for lead-acid, AGM, and LiFePO4 at 12V, 24V, 48V.
How Many Watts in a 12V Battery?
Calculate total watt-hours stored in any 12V battery from its amp-hour rating. Includes common 12V battery examples.
Lead-Acid Battery Runtime Calculator
Calculate lead-acid battery runtime with Peukert effect awareness. Compare flooded vs sealed types for real-world runtime.
AGM Battery Runtime Calculator
Estimate AGM battery discharge time with chemistry-specific defaults. Compare AGM vs flooded lead-acid for your use case.
How Long to Charge a 100Ah Battery?
Calculate charge time for a 100Ah battery from any source: solar, charger, alternator, or generator. Real-world estimates.
Battery Pack Calculator
Size a custom battery pack using series and parallel cell configurations. Enter target voltage, capacity, and cell specs.
CPAP Battery Runtime Calculator
Calculate how many nights your battery powers a CPAP machine. Enter battery capacity, voltage, and CPAP wattage for instant runtime results.
E-Bike Battery Range Calculator
Estimate your e-bike range based on battery size, assist level, terrain, and rider weight. Get instant results for any electric bicycle.
Drone Battery Flight Time Calculator
Calculate your drone flight time from battery mAh, voltage, and power draw. See why real flight times are shorter than manufacturer claims.
Electric Scooter Battery Range Calculator
Calculate your electric scooter range from battery voltage, capacity, speed mode, terrain, and rider weight. Free, instant results.