Two rows in BatteryInfoView’s Battery Information view (F7) do most of the diagnostic work on this site: Designed Capacity and Full Charged Capacity. They sound similar, they are usually shown in the same unit, and the difference between them is effectively the story of your battery’s age. This page defines each field exactly as NirSoft documents it, explains the units you will see — including the optional mAh display — and covers why two laptops of the identical model can legitimately report different numbers. You can follow along with a free copy of the tool from the download page (the main channel there is the official NirSoft file). More background sits in the Battery Health hub.
The two fields, defined
In the official field list, Designed Capacity (field 9) is the full capacity of the battery when it was completely new. It is the manufacturer’s design figure for that battery pack: fixed at the point of design and manufacture, and not something that changes as you use the laptop. Full Charged Capacity (field 8) is the capacity of the battery when it is fully charged — meaning now, in its current condition. That value reflects the battery as it is today, so it is the one of the two that declines over the battery’s service life.
- Designed Capacity: original, when-new capacity. The reference value.
- Full Charged Capacity: current full-charge capacity. The measured, present-day value.
- Current Capacity Value: the absolute capacity right now (field 7), usually in mWh — how much energy is in the battery at this moment, which rises and falls with charging and use.
Keeping Current Capacity Value separate in your mind matters. It answers ‘how much do I have right now?’, whereas Full Charged Capacity answers ‘how much could I have if I charged to full today?’ and Designed Capacity answers ‘how much could this battery have held when it was new?’. Battery Health, covered in Battery Health % Explained, is built entirely from the second and third of those questions.
mWh: the unit both capacities normally use
Both capacity fields are usually expressed in milliwatt-hours (mWh), and Current Capacity Value is usually in mWh as well. A watt-hour is a unit of energy: power multiplied by time. That is why mWh is the natural unit for comparing batteries — it already accounts for the battery’s voltage, so a milliwatt-hour means the same amount of energy regardless of the pack’s design. When you compare a Designed Capacity of, say, 50,000 mWh with a Full Charged Capacity of 42,500 mWh (example figures only, used for illustration), the 7,500 mWh gap is a real energy gap, not an artefact of different measurement scales.
Note the word ‘usually’ in the official descriptions. The documentation consistently says these values are usually in mWh, rather than promising one unit in every case. If your display differs, read the unit shown on your own machine rather than assuming — the ratio between the two capacities, which is what health uses, is unaffected as long as both are read in the same unit.
The optional mAh display, and why it needs voltage
Since version 1.22, BatteryInfoView has an option to display battery capacity in mAh instead of mWh — with an explicit condition in the version history: it works only if the battery voltage is available. That condition makes sense once you separate the two units. Milliamp-hours (mAh) measure electric charge, not energy, and converting between charge and energy requires the voltage: energy is charge multiplied by voltage. Without a voltage value (field 11, shown in millivolts), there is nothing reliable to convert with, so the option simply cannot apply.
For health purposes, neither unit is better. Because Battery Health divides one capacity by the other, the percentage comes out the same whether both values are shown in mWh or both in mAh. Where the choice matters is comparison with other sources: a replacement battery or a manufacturer’s listing may quote mAh, and comparing an mAh figure directly against an mWh figure without converting — using voltage — is a common source of false alarm. When in doubt, compare like with like, and prefer the mWh pair inside BatteryInfoView for the health calculation itself.
Why two identical laptop models can differ
Buyers comparing notes on the same laptop model often find their Designed Capacities match but their Full Charged Capacities do not — or, occasionally, that even designed figures differ slightly between machines. Several ordinary reasons explain this, and none of them require anything to be broken:
- Different histories: Full Charged Capacity reflects use. Two batteries of the same age on paper may have done very different amounts of work, and the field that moves — Full Charged Capacity — records that difference.
- Different individual batteries: A model line can ship over a long period, and the battery fitted is the one that reports the values. The Battery Name and Manufacture Name fields (fields 1 and 2) let you confirm which pack is actually installed.
- Charge state when read: Full Charged Capacity is the capacity at full charge. Readings taken in different circumstances are best compared like-for-like; give the Battery Information view its refresh cycles (it updates every 10 seconds by default) rather than trusting the first paint of the window.
- Genuine unit-to-unit variation: Designed Capacity is a design figure; the battery actually fitted reports its own values. Small differences between individual packs are a property of physical batteries, not a software error.
What should not differ mysteriously is the arithmetic: whatever the pair of values, Full Charged ÷ Designed × 100 must equal the Battery Health shown. If it does not, re-read the fields after a refresh before concluding anything. Our troubleshooting piece Battery Capacity Readings Look Wrong? covers sanity checks for readings that seem off.
Using the pair of values in practice
Together, the two capacities support almost every battery decision on this site. The gap between them quantifies lost capacity in absolute energy terms — often more useful than the percentage alone when judging runtime, because 15% of a large battery and 15% of a small one are different amounts of lost working time. The pair is also the starting point for replacement decisions: When Should You Replace a Laptop Battery? uses them alongside cycle count and symptoms, and How to Choose the Right Replacement Laptop Battery uses the designed figure when matching a new pack.
For tracking the pair over weeks rather than in a single glance, switch to the Battery Log (F8), which adds a status line every 30 seconds by default and can be saved out — see the Battery Log guide and How to Export a Battery Report. All of these readings sit under the Battery Health hub, and the tool itself is on the download page.
Frequently asked questions
Which value should I quote when asking for help?
Quote all three: Designed Capacity, Full Charged Capacity, and the resulting Battery Health %. The percentage alone hides the battery’s size; the absolute pair lets anyone helping you judge both wear and total energy.
Can Full Charged Capacity go back up?
It is the battery’s reported current full-charge capacity, so the displayed value is whatever the battery reports. Small movements between readings are a reporting matter; the long-term direction documented by NirSoft for health is a gradual decrease. BatteryInfoView itself has no feature that restores capacity — see Laptop Battery Calibration: What BatteryInfoView Can and Cannot Do.
Is a bigger Designed Capacity always better?
It means a larger when-new energy store for that pack design. Whether it suits your laptop depends on fit and specification, not size alone — that matching question is covered in the replacement guide linked above.