Hi

Please can you confirm the Make Model and OS, along with any configuration details like touch screen, backlit keyboard, SFF or tower etc etc.

What region of the globe are you in?

Official Dell replacement batteries for the Precision 3561 cost between £55 and £76 including VAT, depending on capacity. Two main options are available: the 4-cell 64Wh (part R05P0) at around £66.35 inc. VAT (£55.29 ex. VAT) and the 6-cell 97Wh upgrade (part 53XP7) at £75.83 inc. VAT (£63.19 ex. VAT).

The Precision 3561 supports both standard 4-cell and larger 6-cell batteries, with the latter confirmed compatible by users as an upgrade (may require no 2.5" drive).

Cheaper compatible batteries from UK sellers start at £39-£58, but opt for genuine Dell for reliability and warranty matching your expertise with Dell hardware.

I suggest the 97Wh battery which lasts longer when the mains fail

NB:  (may require no 2.5" drive)

I take that to mean it clashes with any HDD fitted, so..........