A bad laptop battery can look like a charging problem, a power problem, or just a slow unreliable machine. The first step is separating battery failure from charger, port, board, or software issues.
What causes battery failure
Lithium batteries wear out with charge cycles and age. Heat makes them age faster. Some packs simply lose capacity; others swell, which can push against the trackpad, keyboard, or bottom case.
What the repair actually involves
The laptop is powered down, opened, disconnected from internal power, and the battery is removed. Some are held by screws. Others use adhesive and need slower removal. The new battery is installed, then charging and sleep/wake behavior are tested.
Cost signals
Cost depends on the laptop model, whether the battery is easy to source, and how it is mounted. Common Windows laptop batteries are often simpler. Some MacBooks and thin ultrabooks take longer because of adhesive and tighter internals.
DIY or professional?
If the battery is screwed in and easy to reach, DIY may be realistic for careful people. Glued batteries and swollen batteries are different. Puncturing a lithium battery is not worth saving a small amount of labor.
Repair or replace?
Battery replacement makes sense when the laptop is otherwise useful: good screen, decent speed, enough storage, and no major board issues. If it is already too slow, unsupported, physically damaged, and worth little, put the money toward replacement instead.
What the process usually looks like
Send the model, what happened, symptoms, and clear photos. I quote before starting.