My Dell Inspiron 1525 is now around 4 years old and recently it has not been able to charge and only works when it is plugged in. Also when i start the laptop, it displays a message saying i need to 'reseat the power adapter'. How do i do this? Many Thanks

My Dell Inspiron 1525 is now around 2 years old and works only for 15 or 20 minutes after plugged out.Also on battery symbol, it displays a message saying "consider replacing your battery" and show a cross sign on battery symbol always. How do i do this? Many Thanks

If you are getting a warning message about the AC adapter and you are using a Dell Branded AC adapter, then either the sensing pin in the center of the connector that plugs into the system is damaged, or the connector on the system is damaged. Either way, if the adapter is not recognized by the system the battery charger is disabled and will not charge the battery.
If you can, use a known good Dell AC adapter, see if the error goes away, if it does, then replace the AC adapter with a new DELL Branded adapter (3rd party adapters will run the system but not the battery charger). If a known good or replacement AC adapter has same issue then the power connector/Motherboard on system will need to be replaced.

As you say the system is 4 years old update the bios
your download link is here!
IMP. Be sure to plug in the battery and it should be charges above 10 % and the system should be connected to the mains power supply also ensure there will not be a power outage during the update process
this will resolve the issue 100 %
Dont forget to say thanks!