I plan to get the reference measurement of voltage drop during start which will make is very easy to measure your starter current draw. My wife will go a week driving less then a mile twice a day with no problem of the battery getting low. Not diesel but when temp not low you should not need to use a battery tender to get a reliable start. You need to determine your start current so you won't kill a brand new battery

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)