10.3V is fully discharged. Lead acid batteries should never be fully discharged, or they will be permanently damaged. If the battery has been left sitting at that voltage for any significant length of time, it's probably scrap, regardless of age.Appear to have said the battery is 'holding' 10.3 volts ok
Brand new cars which have been sitting for a few months sometimes need their batteries replacing within the first few weeks, as some folks here who've bought prereg cars have discovered.
Just fit a new battery. If it's reading 10.3V, it's likely damaged beyond repair.A brand new StopStart battery will be in the car for @£100
With the Blue & Me module unplugged, and a new S/S battery, your car will likely be just fine.
If the mileage is still flashing, don't worry, it just needs resetting using a programming tool - there will likely be someone on this forum who can help you with that.
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