I think you mean "The whole rechargable LiPO battery field is relatively new ...".
Low drain rechargable Lithium cells have been around since the late 90's but they aren't cheap, nor are they an easy retrofit if the product didn't originally use them.
Generally its best to replace like with like, for reliability reasons if nothing else, though sometimes cobbling in a battery holder or a higher capacity battery of the same technology makes sense.
For high value test equipment or similar kit that will be a PITA to reconfigure/recalibrate (or worse), one buys the best quality freshest stock leading brand compatible battery available and fit it as originally installed then put a service sticker "Scheduled backup battery replacement" with a date 10 years ahead on the outside of the case. Odds are, it will be someone else's problem and they will be grateful you didn't do a hack job.