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No matter whether it’s in your smartphone or your portable power station, batteries tend to come with heaps of technical specs and jargon.
Without some understanding of the basics, comparing and contrasting different models of battery-powered devices can be challenging.
Storage capacity is one of the most crucial specs to grasp when shopping for a device that relies on a battery. From laptops to solar generators to EVs, knowing how long your device can operate between charges is absolutely necessary to determine if it will meet your needs.
What makes it even trickier is that there are various specs manufacturers use to measure capacity.
Read on to learn about the essentials of battery storage capacity — and ensure you make smart decisions, no matter what kind of device you’re purchasing.
So, What Is Battery Storage Capacity?
Battery storage capacity refers to the maximum amount of electricity a unit can store when fully charged. Not all batteries can be safely operated until fully discharged. For example, you should never discharge a lead acid battery below 50% of its total capacity, as you will shorten its lifespan. LFP batteries can safely be discharged to 80% or lower.
Battery chemistry plays a crucial role in how much run time your battery will actually deliver.
All batteries should have a rating indicating how much energy they can store — including the smallest smartphone batteries, whole home generators, and EVs.
How Is Battery Storage Capacity Measured?
Battery storage capacity is usually measured in watt-hours (Wh)/kilowatt hours (kWh) or milli-amp hours (mAh)/amp-hours (Ah). You can always compare the storage capacity of two batteries with their watt-hours ratings. However, you cannot directly compare two amp-hour ratings if the batteries are at different voltages.
If a battery only has an amp-hour rating, you can convert it to watt-hours using this formula:
Watt-Hours (Wh) = Amp-Hours (Ah) × Voltage (V)
So, a 12V, 100Ah battery could store 1200Wh of energy:
Watt-Hours = 100Ah × 12V = 1200 Wh (1.2kWh)
What Is the Difference Between AC Output (Power) Capacity and Storage Capacity?
Power capacity and storage capacity measure two very different things. If you’re buying something like a portable power station or anything designed to charge or operate appliances, AC output capacity can be even more crucial to making the right purchase decision.
Storage capacity (also known as energy capacity) measures the total amount of electricity a battery can store. The spec indicates how much electricity a battery can deliver over time before needing to be recharged. This metric is usually provided in watt-hours (wH) or kilowatt-hours (kWh) for larger batteries.
For example, batteries with a storage capacity of 2 kWh should deliver 2 kW of power for 1 hour, 1 kW for 2 hours, or any other combination that equals 2 kWh.
Or you could have a whole home generator that offers as much as 25 kWh of combined battery storage — allowing you to run a combined 1 kW of your household appliances and systems for an entire day with power to spare.
AC output or power capacity refers to the maximum amount of electricity (watts or kilowatts) a portable power station or other battery backup system can provide simultaneously. This metric is measured in watts (W) or kilowatts (kW).
AC output is crucial for you to understand for generators and battery backup systems as it determines what appliances you can (and can’t) run — and how many you can run simultaneously.
Another crucial consideration is the starting and running watts of your appliances. Many large appliances, especially ones with motors like refrigerators, ACs, and washing machines, require significantly more power to turn on than to operate. That doesn’t matter When plugged into a wall socket, that doesn’t matter, but if your portable power station or generator can’t supply enough starting watts (surge power), your appliance won’t turn on.
For your reference, here are the average starting and running watts of some common home appliances.
Starting and Running Watts of Typical Household Appliances
|Appliance||Rated (Running) Watts||Starting Watts|
|20” Box Fan||200||350|
Fossil fuel generators can rarely produce more than about 10% of their operating AC output as surge power. On the other hand, battery backup/solar generator systems from EcoFlow can generate up to double their running watts thanks to X-Boost.
What Causes Batteries to Lose Storage Capacity Over Time?
If they’re being used, all batteries lose storage capacity over time. Battery chemistry plays a significant role here. A lead acid battery may last as few as 300 – 500 cycles (charges/discharges) before noticeably diminishing in capacity.
Battery Cycles and Cycle Life
As mentioned above, a cycle means one discharge and a full recharge of a battery.
Most manufacturers provide Cycle Life as a spec that indicates a battery’s lifespan based on usage. A lithium-ion or LFP battery that gets used once a month will last much longer chronologically than one used daily.
Unlike lead acid batteries, Li-ion and LFP batteries suffer minimal degradation due to time — usage that, eventually causes their storage capacity to diminish.
For example, EcoFlow’s award-winning DELTA 2 Max is powered by an LFP battery that offers 2048Wh of storage capacity and 2400W of AC Output ( 4800W surge power). Thanks to X-Boost, it can actually run up to 3400W of appliances simultaneously. X-Boost intelligently adjusts how much electricity it delivers to each device, as many can operate normally without consuming their total running wattage.
Thanks to DELTA 2 Max’s LFP battery chemistry, it will last 3000 cycles before its storage capacity diminishes to 80%. That’s about a decade of daily use — six times longer than other power stations with comparable capacity and output.
Different battery chemistries also have different operating temperature ranges. As a general rule, try to charge your batteries between 50°F – 86°F (10°C – 30°C). Charging at higher or lower temperatures can permanently damage your battery.
Most batteries can discharge safely in a much more comprehensive temperature range. Using DELTA 2 Max as an example again, it can operate safely in temperatures between -4°F (-20°C) and 140°F (60°C).
Depth of Discharge
Depth of discharge (DOD) measures the percentage of a battery’s total storage capacity you can safely use before recharging. The battery will still operate below its recommended DOD, but it can potentially cause permanent damage and diminish a battery’s cycle life. Each type of battery has a recommended DOD to prevent premature degradation. Lead acid batteries have a recommended DOD of around 50%, while LFP batteries can be safely discharged to around 80–90%.
Check with the manufacturer for specific DOD recommendations.
High Discharge Rates
The rate at which batteries discharge can affect their longevity. For devices like portable power stations where AC output varies based on how many appliances you are running, operating constantly at maximum power capacity can suffer heat damage and a shortened cycle life.
When possible, give batteries a break or allow them to occasionally operate at lower electricity loads.
Frequently Asked Questions
Aside from trusting a manufacturer’s published specs, you can also check the storage capacity of a typical battery by using a multimeter to measure voltage. For more accuracy, perform a load test using a battery analyzer. Check the reading against the battery’s rated storage capacity.
Using the integrated smartphone app, you can check how much electricity a solar generator can store (such as the EcoFlow RIVER 2 Pro).
You can increase the amount of electricity you can store by adding more batteries to your system. When connected, multiple batteries form a battery bank. Ensure the batteries are compatible, and exercise caution when connecting them.
You can expand the battery storage capacity of many EcoFlow products, such as power kits and DELTA Series portable power stations, by purchasing additional batteries.
Battery storage capacity is the maximum amount of electricity a unit can store and deliver before recharging.
Don’t mistake this for power (AC Output) capacity, which measures the maximum amount of electricity a battery-powered system can supply simultaneously.
EcoFlow offers a wide range of portable power stations with varying battery storage capacities.
There’s an off-grid electricity solution for any situation: weekend camping, RV living, whole home backup power, and more. Best of all, EcoFlow portable power stations offer solar charging — just add solar panels, and you can generate your own electricity, not just store it.
Browse our selection to find your ideal fit today!