I don't have non-RFTs...yet
But I have this in my car beside the battery:
http://www.slime.com/product/122/Sma...S-PDQ/06).html
Cost about $55 from Autobarn
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Current: 135i Auto, Le Mans Blue - w/ Bridgestone RE-11 rears, GP Thunder 7500k angels, & "golf tee" mod plus a few M3 suspension bits and pieces...