Enter your Device Power, Desired Runtime, and battery details — Battery Type, Max Depth of Discharge, and conditions like age and temperature — and this Battery Replacement Calculator figures out your Required Capacity, Total Energy Needed, and Efficiency-Adjusted Energy.
Required Battery Capacity
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Total Energy Needed
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Energy After Efficiency Loss
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Recommended Battery Rating
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AGM batteries are maintenance-free and handle vibration well, making them ideal for automotive use. Gel batteries work better in extreme temperatures but are more expensive. Flooded batteries are the most affordable but require regular maintenance and proper ventilation.
For lead-acid batteries (flooded, AGM, gel), limit discharge to 50% to maximize lifespan. Lithium batteries can safely discharge to 80-90% without significant degradation. Deeper discharges reduce battery life significantly.
If you're powering AC devices through an inverter, energy is lost in the DC to AC conversion process. Most inverters are 85-95% efficient, so you need a larger battery to compensate for this loss. DC loads don't require this adjustment.
Cold temperatures reduce available capacity by 10-20%, while excessive heat accelerates aging and can reduce lifespan. If your battery operates in extreme conditions, you'll need additional capacity to maintain performance.
Most car batteries last 3-5 years. Replace when it struggles to start the engine, shows corrosion, has a swollen case, or fails a load test. Regular testing after 3 years helps prevent unexpected failures.
Divide your device's wattage by the system voltage to get current draw in amps, then multiply by runtime hours. For example: 60W ÷ 12V = 5A, so 5A × 8 hours = 40Ah needed (before safety margins).
Yes, using a larger battery is always safe and beneficial. It provides longer runtime, reduces discharge depth (extending battery life), and offers reserve capacity for unexpected needs. Never use a smaller battery than calculated.