Car ran great then suddenly battery light came on. I replaced alternator, same thing, but only over 2300 rpm and the airbag light started flashing and wouldn't go into overdrive. Then the overdrive light started flashing. Wtf? Trans fluid changed,new filter. Anything helps

 

What vehicle do you have?

Has the battery been professionally tested?

What charge rate are you getting at the battery?

 

Welcome to the forum

I might add to what grime_reaper asked ... you should do a scan of your OBDII diagnostic connector and retrieve the fault information and pending DTC's. Check you monitors as well for their status.
There will and should be DTC(s) (if the ECU is not corrupt) from the information you posted in your intro here.

 

It's a 2000 Mazda protege lx. Battery is brand new, only thing that comes up on the OBD2 is a faulty O2 sensor

 

Unless you check the battery it really is meaningless that you simply purchased a new battery. There is also a manufactures date on the battery which could indicate how old the battery actually is. This is not the sticker often placed on retail batteries which is more for the sellr or distributor to know the stocking cycle date of the battery.

If the DTC is indicating a O2 sensor then check the connection and also the O2 sensor itself before replacing it.

 

Welcome to the forum