What is the battery replacement # for a pulsar n944 6a00 ?

that looks like a serial number. The 266th watch made in 1978.

Pulsar seem to use a few different batteries.

https://www.google.com/search?q=Battery+for+Pulsar+men%27s+watch+780266

This is the best advice

https://www.fixya.com/support/r27181038-changing_watch_batteries

..

Check out these sites....

https://www.google.com/search?q=vd53-x001+battery+replacement

Takes CR2032 3V Lithium Battery.

Best advice
https://www.fixya.com/support/r27181038-changing_watch_batteries

That model number doesn't follow Pulsar's model numbering scheme and is likely a serial number.

The stock answer is the same battery as the one that is in it.

https://www.google.com/search?q=Pulsar+watch+660137%2C+replacement+batteries

..

Clearly, it is faulty and has some type of parasitic drain. All watch batteries should last a couple of years. My Seiko last for about 3 to 4 years. Return it to Pulsar or a repair agent for repair.

Pulsar Watches - Tell it your way

https://www.pulsarwatches.com.au
Service & Repairs Service Agents Watch Care FAQs Instruction Manuals · Contact. PULSAR. Pulsar. ©2021 Seiko Australia. All Rights Reserved.
‎Watch Care · ‎Customer Service · ‎Abbreviations · ‎Glossary

Pulsar Watches - Contact

https://www.pulsarwatches-europe.com Pulsar burst onto the world watch scene with the first ever LED watch. Ever since, the name has been synonymous with adventurous and leading edge design.

..

Have a read

https://www.fixya.com/support/r27181038-changing_watch_batteries

or

https://www.creativewatch.co.uk/service-and-repairs/battery-replacement-service/pulsar

....

The VX82 X530 battery is a replacement battery for the Pulsar watch. It is a lithium-ion battery with a capacity of 3.7V and 530mAh. It is important to note that you should only use a battery that is specifically designed for your Pulsar watch, as using the wrong type of battery can damage the watch or be potentially dangerous. Always use caution when changing a watch battery.

Yyou can try searching for "VX82 X530 replacement battery" or "Pulsar watch battery replacement" on online retailers such as Amazon, eBay, or Alibaba. You may also check with the manufacturer of your Pulsar watch or a local watch repair shop for replacement options.

This is a complicated repair, not just a battery exchange. Go to a watchmaker. Probably 40 bucks

Take the watch to a jewlers, let him replace the battery they usually only charge for the new battery,
and they do not cost much.