This time of the year I would expect a healthy battery to hold a charge sufficient to start an engine for several weeks +. Provided that there is no drain on it eg power sapping alarm or stuck on courtesy lamp
Winter time with freezing temperature is a far diffrent scenario because Engine Oil thickens as temperature drops, Battery Voltage also drops with temperature. Batterys have to work Harder in cold weather and face far more demands ( heated seats/screens/fans/headlights etc)
A battery that functions ( just) in the summer may well fail to start on the first icey morning.
This is why the RAC/AA etc are always overworked with home start requests when the air temperatures drop below freezing and all the battery prices increase ! ( or discounts dissappear)
These figures relate to 20degrees C 68 F (wikapedia)
12.66 V
6.32 V
100%
12.35 V
6.22 V
75%
12.10 V
6.12 V
50%
11.95 V
6.03 V
25%
11.70 V
6.00 V
0%
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