Disassemble, Clean and re-tighten the jump + post under the hood. Also check and clean the grounds and positive wiring connections to the starter and the alt. Then retest. The jump point gets most of the failed issues. Also, check the grounds points near the battery for poor connections.

Look up Volt drop testing for a quick measurement of how to test these points.

Examples
https://www.aa1car.com/library/voltage_drop_testing.htm
https://www.youtube.com/watch?v=qPpHRuddhh4

__________________

2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green