You have an almost brand new Ryobi battery that the charger won't recognize and won't charge. Here's how to fix that.NOTE: Before doing all this, first try to pulse charge your battery by plugging and unplugging your charger (with the battery in it) for 10 seconds. Try this a few times. If it doesn't correct the problem, continue on with this tutorial.
An AC adapter (12 volt or more for an 18 volt battery fix)
Star head screwdriver
Cut the end off of your AC adapter. That's right. Just cut it off. It's for a 10 year old cell phone, you're never going to use it again anyway. It's frankly kind of weird that you saved it to begin with.
Separate and strip off 1" of each wire. You have *just* made booster cables! Good for you.
Remove the screws holding the battery together. There's a hidden screw under a piece of plastic. You need to pry the plastic off to get at the screw underneath. I used a very thin screwdriver to pry it off.
Pull the top off of the battery case.
Remove the 2 plastic side pieces. They're the things you press in to remove your battery from your drill.
Lift the battery pack out.
Set the Multimeter to read volts. For testing an 18 volt battery choose the 20 volts setting. This will give you the most accurate reading. (If you don't have a multimeter skip to Step 9 and hope for the best)
Touching the red probe to the positive (red) terminal and the black probe to the negative (black) terminal, read the voltage shown on the multimeter. In my case the battery was carrying a charge of 0.06 volts. Which is *almost* nothing, but not completely nothing.
Plug your AC adapter in and using the wires, boost your dead battery. Just touch the black wire to the negative terminal (the one with the black wire going to it) and the white wire (or striped wire) to the positive terminal (the one with the red wire going to it). Do this on and off for approximately a minute. DOUBLE CHECK THAT YOU ARE TOUCHING POSITIVE TO POSITIVE AND NEGATIVE TO NEGATIVE.
Test your the voltage on your battery pack again. It should be higher than it was before boosting. IF IT IS NOT, THEN STOP. YOUR CELL COULD BE DAMAGED AND CONTINUING COULD BE DANGEROUS.
Put the plastic cover back on the battery pack (just the part that goes into the charger) and set your battery on the charger to see if it will take a charge. If you still only get a red flashing light and the battery won't charge, boost the battery some more. I find the battery charger will recognize that the battery is good again when you boost it to between 10 and 14 volts.
Repeat the "pulse" boosting and testing the battery until it will finally be recognized by the charger and you get the green light.
Reassemble your battery. Your rechargeable battery is now fixed.
Black wire = negative Striped or solid white wire = positive It is very important to not mix the two up.
There's a hidden screw under a piece of plastic. You need to pry the plastic off to get at the screw underneath. I used a very thin screwdriver to pry it off.
Volts are symbolized by a "V" with one or two straight lines over it on a multimeter so it's that section of the multimeter that you use. The section under the V with the straight line(s). Not the squiggly line. The straight line.
Lithium ion batteries need to be "pulse" charged. Which means you hold your wires down for 15 seconds or so, then release them. Then hold them down again. Over and over.