This is what I use from Princess Auto.
https://www.princessauto.com/en/detail/spf1-automatic-battery-charger-extender/A-p8487332e
I picked up 2 using one on my Boxster full time all winter and during driving season if the car sits for any length of time and one on my Fusion since it isn't driven as much in the winter. These will not overcharge and have proven very reliable.
I got them both when Princess had them on sale for about $45.00 CDN I believe a couple of years ago.
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