Battery Tender is a brand name.
I have several of their units and they have worked quite well, sometimes on a battery for years (generator). The BMW battery charger is a Battery Tender, with BMW logo and higher price.
I just hook one up to the terminals under the hood with the clamps.
'95 Alpine M3 LTW
'00 Dakar M Roadster
'02 Topaz M3
Red/White SRF #4 (Chassis 561)