How long should i charge my new black and decker 18v battery

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: Some Ryobi 18v batteries charge, others don't.

Had the same problem with some makita batteries, Was going to throw them away so decided to take apart and see what was happening. The are made up of 1.5 volt cells soldered together, found that many had .9 volts or less and others had 1.5 or more. This means that some of the cells had gone bad (probably due to lack of chemical reaction). Found that if I collected all of the 1.5 volt together could charge just fine. Problem is it is very hard to get them all soldered back together and even harder to enclose them. If a mfg. could come up with some way to change cells individually they could make a lot of money and save us a lot. So the answer to your question is buy you at least one more battery and recycle your old one.

SOURCE: lost 18V AC adaptor- can I use one made for laptop with 18V output?

I don't know if I would try this or not. there could be a difference in the amps and usually a charger is designed to shut off or go to trickle when the battery is fully charged.

SOURCE: light on ryobi 18v charger

More than likely a defective battery sinse the other ones charge fine..
Bring it back for exchange of another one..

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SOURCE: fixing a cordless drill battery charger

usually transistors have three legs, diodes have two arms all very confusing isn't it? resistors have two arms as well but not three legs or only two legs and no arms its all about arms and legs isn't it do not attempt this repair if you live at home