Runtime has dropped and you want to know whether the battery is worn or whether something is draining it. Your laptop has been recording the answer since the day you bought it, and getting at it takes one command.
The short answer
On Windows, open a command prompt and run the battery report command, which produces an HTML file showing design capacity against current full charge capacity and a history of both. Below about 80 percent of design capacity the battery is meaningfully worn; below 70 percent it is due for replacement. On a Mac, the battery condition and cycle count are in system information.
Generating the report
On Windows, open a command prompt and run powercfg /batteryreport. It saves an HTML file and tells you where. Open it in a browser and look at three things:
- Design capacity. What the battery held when new.
- Full charge capacity. What it holds now.
- Cycle count. How many full charge cycles it has been through.
The report also includes a usage history and a battery capacity history going back months, which shows the decline over time rather than a single snapshot. That trend is more informative than the current number, because it tells you whether the decline is steady or has accelerated.
On a Mac, hold Option and click the Apple menu, choose System Information, and look under Power. You get cycle count and a condition rating.
What the numbers mean
- Above 90 percent of design capacity: healthy, typical of a battery under two years old.
- 80 to 90 percent: normal wear. You will notice shorter runtime but nothing is wrong.
- 70 to 80 percent: meaningfully worn. Most manufacturers consider this the end of the warranty threshold.
- Below 70 percent: replacement is worth doing. Runtime is roughly two thirds of new and declining faster.
- Below 50 percent: the laptop is effectively a desktop. Expect unexpected shutdowns under load.
Cycle count matters too. Most laptop batteries are rated for somewhere between 500 and 1000 full cycles before falling to 80 percent. A battery at 400 cycles and 75 percent capacity has worn faster than expected, which usually means heat.
Generate the battery report
Run the report command and read design capacity against full charge capacity. This is the objective answer, rather than an impression based on how long it seems to last.
Look at the capacity history, not just today's number
The report shows the trend over months. A steady gradual decline is normal ageing; a sharp drop suggests heat damage or a fault.
Check the cycle count against the rating
Look up your model’s rated cycles. High capacity loss at a low cycle count points at heat or long periods sitting at full charge rather than normal use.
Enable a charge limit if your laptop offers one
Many laptops can cap charging at 60 or 80 percent. For a machine that lives on a desk plugged in, this substantially slows ageing, because sitting at 100 percent is one of the harder things you can do to a lithium cell.
Keep it cool
Heat is the main factor in battery ageing. Do not use it on a bed or a sofa where the vents are blocked, and do not leave it in a hot car. This matters more than any charging habit.
Avoid leaving it flat for long periods
If you are storing a laptop for months, charge it to about half first. A battery left at zero for a long time can fall below the voltage it will ever charge from again.
Check what is draining it before blaming the battery
If capacity is healthy and runtime is still poor, something is consuming power. Look at the battery report’s usage section and at what runs at startup.
Get a quote before deciding
Battery replacement varies enormously by model, from a simple clip-out to a full teardown. The part is usually inexpensive; the labour is what differs.
The charge limit feature is the single most effective thing you can do for a laptop that lives plugged in at a desk. A battery held at 80 percent ages considerably more slowly than one held at 100 percent, and for a machine that rarely runs on battery you lose nothing you actually use.
Myths worth discarding
- You should fully discharge it regularly. This was true of nickel batteries decades ago and is actively harmful to lithium ones. Partial charges are better.
- Leaving it plugged in destroys the battery. Modern laptops stop charging at full and run from mains. The real harm is sitting at 100 percent while hot, which a charge limit addresses.
- Calibrating it improves capacity. A full discharge and recharge cycle only recalibrates the percentage reading. It does not restore capacity and it puts the cell through a full cycle.
- Removing the battery when on mains is better. On machines where it is removable, storing it at full charge in a drawer is worse for it than leaving it in a laptop that manages it.
Check whether the laptop still sits flat on a table. A base that rocks, a raised trackpad, or a lid that no longer closes flush means the battery has swollen. That is a fire risk, it will eventually crack the case or the screen from inside, and it should be replaced promptly rather than at your convenience.
When to replace
Replacement makes sense when capacity is below about 70 percent and the laptop is otherwise good, when the battery has swollen at any capacity, or when the machine shuts down unexpectedly under load. It makes less sense on a machine you were planning to replace anyway within the year.
Before paying, check the warranty. Batteries are often covered for a shorter period than the rest of the machine, but a battery that has fallen below the manufacturer’s threshold within that period is usually a valid claim.
How do I check laptop battery health on Windows?
Run the powercfg battery report command from a command prompt. It produces an HTML file showing design capacity, current capacity, cycle count and a history of the decline.
What capacity means I should replace the battery?
Below about 70 percent of the original design capacity. Between 80 and 90 percent is normal wear on a battery a couple of years old.
Is it bad to leave a laptop plugged in?
Not in itself, since modern laptops stop charging at full. What ages the battery is sitting at 100 percent while warm, which is exactly what a charge limit setting addresses.
Should I fully discharge the battery sometimes?
No. That advice applies to battery chemistries from decades ago. Full discharges are harder on lithium cells than partial ones.
What if the laptop does not sit flat anymore?
The battery has swollen. Stop charging it, have it replaced promptly, and do not press on it. It is a fire risk and it will eventually damage the case or screen from inside.
The bottom line
Run the battery report and read full charge capacity against design capacity, because that is the objective answer rather than a guess. Look at the trend as well as today’s number. Enable a charge limit if the laptop lives on a desk, and keep it cool, since heat matters more than any charging habit. And check it still sits flat, because a swollen battery changes the urgency entirely.
