That is basically the same thing. They both run out of charge after a while and you lose your saves.
Between super capacitors and Tennokoe banks, the PCE has the best of both worlds when it comes to protecting save files. I keep a TG w/Turbobooster Plus, a Duo, and a SGX w/SCD hooked up in my living room. If I don't play one for a month, I just turn it on for a minute - capacitor charged. We never have to buy replacement batteries and no one's system has ever been destroyed by dead batteries.
For extra storage and really important files, we have Tennokoe banks. They hold 4x as much as a Duo, they cost $8 (only slightly more than a single button battery at Radio Shack), and their batteries are lasting longer than some of the ones in my SNES carts.
We're also lucky that half of our games (hucards) feature passwords. A hassle for everyday use, passwords are good for freeing up system space after beating a game and protecting long-term accomplishments. I still have my Order of the Griffon and Ys passwords for right before the last battles.
The Duo save system does have flaws - I've lost files by forgetting to turn my system on AND being too lazy to mirror a bank onto a Tennokoe card for six months. It's a responsibility vs. reliability trade off. IMO, a little mindfulness and elbow grease is worth not having to screw around with batteries.