I've been using Yuasa battery maintainers on Odyssey batteries for about 12 years (including the mini-beef PC680) - 1 amp and float mode at 14.4 volts. Never had a problem even when the charger was on a battery for many months at a time. I also use these chargers on regular, flooded cell batteries of all sizes, and very small, AGM batteries that make the PC680 seem big by comparison.
Why the recommendation for a 12V charger for the small Odyssey batteries?
Here's the Yuasa -
https://www.amazon.com/Yuasa-YUA1201000-Automatic-Battery-Maintainer/dp/B00HZTDKZG/ref=sr_1_4?crid=1GRQB6V19MKZX&keywords=yuasa+battery+tender&qid=1577500879&sprefix=yuasa+battery+tender+%2Caps%2C323&sr=8-4