I got this cheap bluetooth obd2 connector which works with my (android) Dr. Prius app:
https://www.amazon.com/Veepeak-Bluet...dp/B011NSX27A/
For free, the Dr. Prius app itself lets you monitor nearly useless bar-graphs of the individual cell voltages. For a fee you can run more involved tests to diagnose potentially bad cells and/or estimate remaining battery pack life. I haven't purchased one yet, but I think it is like ~$10 to test on 3 cars or ~$20 to test on unlimited cars.
Your gen2 never came from the factory with a lithium ion battery although Toyota did test it in the gen2 and ultimately decided to stick with NiMh (
https://seekingalpha.com/article/161...-for-the-prius ).
The gen3 plug-in Prius uses lithium ion.
Gen 4 generally uses lithium ion, but Toyota still uses the higher weight, older technology NiMh batteries in the awd Prius because it assumes the AWD prius will be used in colder climates (where NiMh outperforms Li+). I've read that certain Canadian Prii also use NiMh for that same reason.
Dr. Prius does offers a Lithium Ion "upgrade" battery pack for ~$2200 with a 2 year warranty:
https://projectlithium.com/products/...placement-pack
It is relatively new so we haven't seen any independent long term results.