I can't remember what light flashes but our makita charger occasionally stops working and it's because the fan isn't running, take it to bits blow out with airline and away it goes again, its needing done more often now so could be on its way out.
Just plug it in, the charger reads the info on the chip in the battery, if the chip says battery is hot then you get cooling fan when charging. Sometimes the chip/ charger get a bit out of sync but usually kiss and make up after the next cycle.
you hear mixed reports about the copies. I always get Genuine never had a problem. Early days of the LXT had issues with the cell that monitored the balance running too far to recover but its not a problem now
6ah have had a few fires.
(Makita Talk Group on FB- for info and deals https://www.facebook.com/groups/167031360437573/?ref=bookmarks )
paid < £100 for 2 genuine 5a/h last month, no blackfriday deal no discount code they will last me 3/4 years of almost daily use
are you still having trouble with one battery? stick it in a drill run it for a minute and stick it back on charge should clear any problems