Charge battery until it floats on the charger your using. Use a volt meter to read static voltage
Results over 13v?
Less than 12.5?
Who the hell knows? (Too low and falling?)

If the 1st one install battery and finish work. The vehicle will run on the battery only if the charging system is out to lunch.
When you time there is a complete electrical test approach that will uncover the issues:
Battery not likely based on your postings
Charging system
Wiring issues/ system draw when off

quick test After the battery is fully charged.
Car off battery tested at terminals
Voltage?
Start car
Test same way and read voltage
Increase in readings?

Post the answers

Helpfull?

__________________

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