On a Laptop you have tho batteries:
- A small, non rechargeable (normally a coin CR2032, 3V battery) to support BIOS settings and the real hardware clock.
- A big rechargeable battery.
When the external power supply is on or the main battery is charged, the A small, non rechargeable (normally a coin CR2032, 3V battery) is bypassed.
Normally the coin battery will last 5 ~8 years.
Try to shut down the laptop, remove the external power supply
and the main battery. Wait 1/2 hour and then reinstall the external power supply and the main battery. Boot and enter BIOS.
If time has changed you need to replace the (BIOS & clock) coin battery.
On most Laptops, to replace the coin battery isn't a simple task. You will need to disassemble all laptop to be able to get to it.
On most Laptops, the coin battery isn't on a socket. It's soldered on a wire with a connector.
First of all, download the service and maintenance manual and find what you're going to need.
https://downloads.dell.com/manuals/...notebook/vostro-a860_service manual_en-us.pdf
If you have a small soldering device (~30W) you can remove the wires from the old battery and solder to the new one. (page 9 - Coin-Cell Battery). Then isolate it with a thermal shrink tube or with isolation tape.
As you open the laptop, clean it all, specially the fan and heat sink. Sometimes you're able to remove the fan without removing the heat sink. Don't remove the heat sink from the CPU.
