How can I get extended battery life for old Samsung laptop?

I cannot answer your questions.
My situation is the same as yours - a laptop with its main battery inside its casing.

A Powerbanks with 19V outputs do exist. I have them for my Dell Inspirons.
- You also need to note the current provided by your existing power supply adapter and take that as the minimum current that must be provided by any powerbank you consider. You can assume that they made that to provide the current that is necessary to both power the computer & recharge its battery at the same time.
- The powerbank must also have the appropriate input & output connectors. So, just for example, it would be a big coincidence if my 19V, 2.3A powerbank would be suitable for you.

I suggest you try searching for suitable powerbanks
- In the Samsung website
- In something like Amazon you could search for Samsung Series 7 Ultra Notebook powerbank but make sure you find an explicit reference to your model in any product page you look at [Amazon is liable to give you lots of results for inappropriate powerbanks]. Personally, I wouldn't go ahead unless there was also a review by a user of the computer model confirming that it worked - that it connected correctly, powered the computer & recharged its battery.

B You're talking about a UPS.

C.1 I suggest you check the Samsung website for a "service manual" for your model. That should include instructions for replacing the battery.

C.2 If it is replaceable then check the Samsung site to get the part number of the battery or use the service manual to take off enough for you to read the battery part number off it. Just for example, my battery part number is 33YDH
Then you can search Amazon etc. Again, I'd check for an explicit reference to your computer model and a review that says it fits.
When I used Amazon for a replacement battery to fit in my Dell Inspiron 7779, I waited until I found one that claimed to be 'genuine' Dell and was sold by Amazon / sold by someone else but fulfilled by Amazon so that I could rely on a recognised firm if I had problems with it.



Best of luck,
Denis

ship69 said:

My only real problem is that is battery life.
...New battery? What are my options for buying an new battery for it with a larger capacity?
How difficult is it to replace the battery (i.e. is it soldered in?)

Firs check the battery's capacity. With use it will wear out and loose capacity. Run a Battery Report, and replace if significantly less than design capacity. You don't necessarily need a higher capacity battery, not if your current one has worn out.

Generate Battery Usage Report in Windows 10

No, it's not soldered in. Remove the back cover and you can replace the battery.

Samsung ATIV Book 7 NP740U3E-K01UB Battery Replacement - iFixit Repair Guide

samsung np740u3e battery - Google Search