I use the 1.5 amp Schumaker tender from wally world for about $20. I have 12 of them running in the garage now. I have used them for years. Evan ran over two of them and they keep going.
I hook directly to the battery terminals. The recommended procedure is to leave the tender on until you leave the garage and reconnect when you return. This is the only way to get the maximum life out of the battery. I only exclude the DD as it does get used more than once a day.
I have had a motorcycle battery that typically last 2 to 3 seasons go for over 7 years before I sold the bike.
I've also used the little HF one and it did work but not after I stepped on it.
I've had some of the Schumaker's so long that they were $18 at wally world. So much for falling prices.