AC Runtime on Battery: What are the Exact Hours for 5-15kWh Systems

A. Your Air Conditioner's (AC) Specifications

Power Consumption (Watts or Kilowatts - kW):

This is the most critical factor. The more power your AC unit draws, the faster it will deplete your battery. You can usually find this on the AC's specification label (often listed as "Cooling Capacity Input Power" or similar) or in its manual.

BTU Rating and SEER/EER:

Higher BTU (British Thermal Unit) ACs generally cool larger spaces but consume more power. However, look at the SEER (Seasonal Energy Efficiency Ratio) or EER (Energy Efficiency Ratio) ratings – a higher SEER/EER means the AC is more efficient and uses less electricity for the same amount of cooling.

Variable Speed (Inverter) vs. Fixed Speed ACs:

Inverter ACs are significantly more energy-efficient as they can adjust their cooling output and power draw, consuming much less power once the desired temperature is reached. Fixed-speed ACs run at full power until the thermostat turns them off, then cycle on again, leading to higher average consumption.

Startup (Surge) Current:

AC units, especially older fixed-speed models, draw a much higher current for a brief moment when they start up (compressor kicking in). Your battery system and inverter must be able to handle this surge power.

B. Your Battery Storage System's Characteristics

Battery Capacity (kWh or Ah):

This is the total amount of energy your battery can store, typically measured in kilowatt-hours (kWh). The larger the capacity, the longer it can power your AC. If capacity is listed in Amp-hours (Ah), you'll need to multiply by the battery voltage (V) to get Watt-hours (Wh), then divide by 1000 for kWh (kWh = (Ah * V) / 1000).

Usable Capacity & Depth of Discharge (DoD):

Not all of a battery's rated capacity is usable. The DoD specifies the percentage of the battery's total capacity that can be safely discharged without harming its lifespan. For example, a 10kWh battery with a 90% DoD provides 9kWh of usable energy. BSLBATT LiFePO4 batteries support up to 90% depth of discharge on residential models, allowing more of the rated capacity to do actual work. This matters when sizing for AC runtime.

Battery Voltage (V):

Important for system compatibility and calculations if capacity is in Ah.

Battery Health (State of Health - SOH):

An older battery will have a lower SOH and thus a reduced effective capacity compared to a new one.

Battery Chemistry:

Different chemistries (e.g., LFP, NMC) have different discharge characteristics and lifespans. LFP is generally favored for its safety and longevity in deep cycling applications.

C. System and Environmental Factors

Inverter Efficiency:

The inverter converts the DC power from your battery to the AC power your air conditioner uses. This conversion process isn't 100% efficient; some energy is lost as heat. Inverter efficiencies typically range from 85% to 95%. This loss needs to be factored in.

Desired Indoor Temperature vs. Outdoor Temperature:

The greater the temperature difference your AC needs to overcome, the harder it will work and the more power it will consume.

Room Size and Insulation:

A larger or poorly insulated room will require the AC to run longer or at higher power to maintain the desired temperature.

AC Thermostat Settings & Usage Patterns:

Setting the thermostat to a moderate temperature (e.g., 78°F or 25-26°C) and using features like sleep mode can significantly reduce energy consumption. How often the AC compressor cycles on and off also impacts overall draw.