Old school 1.25 amp Battery Tender brand on all the cars when they sit for more than a couple of weeks. Works fine through the under hood charge/jump lugs on the e53, e46, e39 and e90; all are AGM and 6-8 years on a battery typical using Interstate from Costco when possible, Diehard, Duracell, Deka as alternates. Recently replaced a 15 year old Interstate in an infrequently used ‘82 MB when I realized how old it was though still working and testing fine. You all probably know this but 3 or 4 companies make nearly all the batteries is the US so comparing current specs and price versus buying by brand matters. Also, be careful about buying chargers on eBay and other sites, bootlegs are out there and look real including packaging but are not, I learned the hard way. Check with the charger manufacturer regarding which sites sell legit product.

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Garage
'05 X5 4.8is Imola Red/Black
'02 330Ci Conv. Electric Red/Tan
'01 M5 Lemans Blue/Black/Silverstone
'00 528 Electric Red/Grey
'07 BMW 328iX Silver/Black
'82 Mercedes 380SL Signal Red/Grey
'73 VW Beetle Convertible (restored)
'17 Honda Odyssey
'98 Volvo V70 GLT
'94 Ford Explorer XLT
'11 Honda Accord V6 Manual Coupe (bought Fall 2020 from American Honda with 250 miles)
'98 Volvo V70 T5 (project)