I did not get it from Amazon but I got this battery charger yesterday:
https://www.amazon.com/Smarter-Tools.../dp/B075FWXK9N
I haven't used it yet but the manual specifically says it can be used to maintain voltage during battery replacement. It comes with three ways to hook it up, regular clips, ring terminals, and accessory "cigarette lighter" plug. The latter would seem to be handy to maintain voltage. It also is made to be left on a car for extended periods.
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128i Convertible, MT, Alpine White, Black Top, Taupe Leatherette, Walnut, Sport
Ordered 5/22/09, Completed 6/4/09, At Port 6/9/09, On the Georgia Highway 6/13/09, Ship Arrived Charleston 6/24/09 at 10pm, PCD 7/21/09
