Espace 2.2 dci lack of power

hi just brought this car and only few miles down road the battery light has came on and no power not go uphill unless you stop and rev car high then pull off

1/

it done 140k mile it and 51 plate 02 year been told alternator is faulty but is it coomon to lose power like this when battery light / stop light comes on dont want to spend more on car if it is something else

2

as it also has oil leak on crack shaft seal would this have a underline problem to course seal to go ?