The Makita BL1815 battery will not charge, lights flash red/green, indicating bad battery. I replaced one open cell with known good cell, charger still reads bad battery although I can charge from an alternate source when bypassing the too-smart circuit board. Can a bad battery message stored in memory in an I/C on circuit board be reset? Thanks, Tim A

SOURCE: makita dc1804f charger will not charge new i-mh 1834 18v battery

I think your tryiong to charge NIMH batteries oon a charger designed for Lithium Ion batteries. With all the new style batteries such as NICAD, NIMH and LI-ION, charging becomes difficult. Most chargers pre NIMH and LI-ion, were designed for NICAD's. The best advise, match your batteries with the correct charger

SOURCE: Battery Issues

When Li-Ion batteries are discharged to a too low voltage (below 2,75 V/cell, in this case 13,75V) the charger will assume that the battery is damaged, and will not charge the battery. First measure the battery voltage with a volt meter, if the voltage is significally below the 13 V the battery are no good. If you have a reading of lets say around 10 V, you can raise the voltage shortly on the battery, by jumping it with a fully charged battery. Connect the "-" poles on each battery. After this, shortly connect the "+" poles, for no more than 5 seconds,disconnect the wires and immediatly put the battery in question in the charger. If it starts charging, every thing if fine. If not, try the process again, you might wanna recheck the voltage if it rises.
Please be aware, that over discharging Li-Ion batteries, will lead to damage of the Li-Ion cells, which results in loss in capacity, therefore, if you are not to use your Li-Ion tools for a while, make sure the batteries are fully charged.

Hope you guys could have sucess with the above

Best regards
Soeren

SOURCE: MAKITA LXT BATTERY CHARGER

hey
flashing orange=cooling abnormality.
you need to wait for the battery to cool.

see my mod page, it has all light explanations in it.
Have fun
Avi

SOURCE: Brand new Makita DC18RA charger wont charge the batteries.

Return to store for replacement.

SOURCE: When putting the battery in

Have you tried just waiting a few minutes, it might start to charge anyway. But if not, is there some reason you would assume that you don't have a bad battery? There are lots of bad Li-Ion batteries.