Been having this issue on and off for a week

Drove all around Wednesday so Battery had to be fully charged. Put car in garage at 1pm, get in car at 5:45 started right up no issues. Got there shut car off brought Jordan in sat in car with it off no radio or anything played on phone 7:30 go to start car and all lights dim and just here a click. Time and dates all erased and car won’t start…WTF really. Nothing saying high battery drain or anything! Got home put in garage put battery charger on car 2amp charge for an hour and it was 90% charged when I took it off before bed. Maybe I got a junk battery? It holds a charge but can’t maintain it, like a bad cell but not bad enough to show its junk? Bmw factory battery is an excide and I replace with excide, had guy double check me on specs when I bought it as I did my research on their site to make sure I had same CCA amps and all…identical battery new in April

Last night went to sears sat for hr. car wouldn’t start. Jumped car went home (less than 2 miles) . let car run got volt meter and tested and running a solid 14.2-14.3. shut car off checked battery running a solid 12.4v and slowly went down .001 every two-three second. Looked back in 10 mins. Went back to 12.4, get in hit start button and nothing heard click of starter lights dim jump out put meter on battery 10.5 volts??? Then 9.5 (ignition on) jumped car drove less than 2 miles got battery load tested said it was fine…got in car hit start button and starts??? Okay get home put 2amp charge hr. later full charge. This morning put meter on battery (alarm on all night sitting in my garage so warm in there) read 11.97v and went hit started click, lights dim go to battery again 10.1v. going to get battery replaced not sure why something is drawing 2 full volts out of a battery when starting seems not likely as it’s not 20 degrees out and it doesn’t sit outside. SO ideas??? Uggg swapping battery under warranty hop it’s bad cell even though the load test said it’s fine.

 

I would get the battery tested again. The 2 volt loss could be simply that the battery is weak or a bad cell. The high amp load of attempting to start the car causes a rapid drain. If it checks good you most likely have some sort of parasitic drain when the car is sitting. You could then put your multimeter in series with the battery and measure how many amps it draws when not running.