What is an "Ni-Cr" battery?
There is no such battery called Ni-Cr. It is likely just a typo.

As other commenters have mentioned the 'r' and 'd' are close on the keyboard.

The only common nickel based battery chemistries are Ni-Cd (or Nickel Cadmium) or Ni-MH (Nickel Metal Hydride).  They operate similarly with Ni-MH being the more recent with better capacity and not using toxic Cadmium. They both have terminal voltages of ~1,2v which is similar to zinc-carbon (manganese alkaline) primary batteries.  They are relatively safe and do not usually suffer from explosive or thermal failure in the way that Li-Ion batteries do.

They both suffer from high self-discharge rates of many % per month and have been supplanted in modern equipment by Lithium based batteries (e.g. Li-Ion).