How do I find details about my battery in my Windows 10 laptop / tablet?

In both cases you can get the information about your battery (especially if you want to replace it) using the power configuration command as in:
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C:\Users\powercfg /?
You get the help for power configuration as shown here:
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C:\Users\Jayaram>powercfg /?
POWERCFG /COMMAND [ARGUMENTS]
Description:
  Enables users to control power settings on a local system.
  For detailed command and option information, run "POWERCFG /? "
Command List:
  /LIST, /L          Lists all power schemes.
  /QUERY, /Q         Displays the contents of a power scheme.
  /CHANGE, /X        Modifies a setting value in the current power scheme.
  /CHANGENAME        Modifies the name and description of a power scheme.
  /DUPLICATESCHEME   Duplicates a power scheme.
  /DELETE, /D        Deletes a power scheme.
  /DELETESETTING     Deletes a power setting.
  /SETACTIVE, /S     Makes a power scheme active on the system.
  /GETACTIVESCHEME   Retrieves the currently active power scheme.
  /SETACVALUEINDEX   Sets the value associated with a power setting
                     while the system is powered by AC power.
  /SETDCVALUEINDEX   Sets the value associated with a power setting
                     while the system is powered by DC power.
  /IMPORT            Imports all power settings from a file.
  /EXPORT            Exports a power scheme to a file.
  /ALIASES           Displays all aliases and their corresponding GUIDs.
  /GETSECURITYDESCRIPTOR
                     Gets a security descriptor associated with a specified
                     power setting, power scheme, or action.
  /SETSECURITYDESCRIPTOR
                     Sets a security descriptor associated with a
                     power setting, power scheme, or action.
  /HIBERNATE, /H     Enables and disables the hibernate feature.
  /AVAILABLESLEEPSTATES, /A
                     Reports the sleep states available on the system.
  /DEVICEQUERY       Returns a list of devices that meet specified criteria.
  /DEVICEENABLEWAKE  Enables a device to wake the system from a sleep state.
  /DEVICEDISABLEWAKE Disables a device from waking the system from a sleep
                     state.
  /LASTWAKE          Reports information about what woke the system from the
                     last sleep transition.
  /WAKETIMERS        Enumerates active wake timers.
  /REQUESTS          Enumerates application and driver Power Requests.
  /REQUESTSOVERRIDE  Sets a Power Request override for a particular Process,
                     Service, or Driver.
  /ENERGY            Analyzes the system for common energy-efficiency and
                     battery life problems.
  /BATTERYREPORT     Generates a report of battery usage.
  /SLEEPSTUDY        Generates a diagnostic connected standby report.
  /SRUMUTIL          Dumps Energy Estimation data from System Resource Usage Monitor (SRUM).
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One of the arguments is 'batteryreport'.
Now if you type as shown here:
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C:\Users\Jayaram>powercfg /batteryreport
Battery life report will get saved to C:\Users\Jayaram\battery-report.html.

Type as shown below, the HTML file will be launched in a browser.
C:\Users\Jayaram>battery-report.html
C:\Users\Jayaram>

Your battery report is saved to a html file.  This file is launched when you run the command, battery-report.html as above.
Here is the generated file (only partly shown):

These are the main sections in the report:

Battery details
Installed Batteries
Recent Usage
Battery Usage
Usage History
Battery Capacity History
Battery Life Estimates

It may be interesting to run this file once in 3 months and keep a record. When you are not using you can switch off (for long expected durations of inactivity), or let it sleep (for shorter durations of inactivity). Adjust your battery saver settings in Windows 10 Settings.