Battery Woes

[Apex Everything]

How can I tell it is truly time to replace my battery?

I have an interesting chain of events which would probably de-charge any cars battery, so I am having trouble determining if I should pull the trigger on a new battery.

End of March, I let my car sit for 4-5 days no charger (before I received one) because of a nail in the tire. My position allows me to work from home 2-3 days a week or for emergencies (car issues, snow etc.) so letting the car sit had no effect on my life.

When I drove the car to the tire place to install my new tires I received the dashboard alert for battery drain. I got my tires done and then borrowed my father in laws charger and let it charge overnight. Since then never had a dashboard alert for battery drain.

The first 3 weeks of April my car was at BMW to have engine warranty work done. During that time I can imagine it was not driven or started up often. Even after the work was completed. So 3 weeks of my M3 battery draining with little to now charge build up from my driving.

Again, since the one time I had the battery alert I have had no dashboard messages.

I obtained a Optima 400 battery charger, this charger analyzes your battery and tells you its charge level from 0-100%. When I hooked it up to the M3, it read as 25%.

I am worried, but the car sat for half a month, so I am thinking it just needs some constant recharge.

Some more background, I bought the car used and it is a 2012. I can only assume it is the first battery in the car.

My battery knowledge is lacking so I am thankful for any insight or opinion.

If it goes south, I am thinking about getting a Brallie 21 battery, can you also suggest any performance battery options in the $200-300 range? I do not want to put just any consumer level battery in a M3, #BecauseM3

Your thoughts......?