I have a Black & Decker EPC128 12V cordless drill. It has two batteries. Since the recharger has no light or indicator on it, I never surely understand whether the battery is partly/fully charged or overcharged. How long exactly should I recharge the batteries? The tool is something like this:


  • 1
    Does it not say in the instruction leaflet?
    – ChrisF
    Mar 2 '12 at 22:22
  • 1
    A search for the model number might turn up the instructions online.
    – ChrisF
    Mar 2 '12 at 22:24
  • 3
    Wow, that's a major design flaw - no blinky light!
    – Doresoom
    Mar 2 '12 at 22:47
  • 1
    Yeah, I would have issues with no blinky light, especially as some batteries (NiMH) can be overcharged which will shorten their lifespan. My Ryobi ONE+ NiMH charger has TWO blinky lights (!) and it's a smart charger that'll go into trickle-charge mode to protect a battery that's left in it overnight (or longer).
    – KeithS
    Mar 5 '12 at 16:06
  • 4
    Pretty sad as overcharging kills NiCad and NiMH batteries. There are many specialized chips that understand the charge cycle of both these battery chemistries and can sense when the maximum charge is reached and the cycle is complete for termination. Even cheap Chinese knockoff stuff includes smart charging. It's one of the reasons I've moved away from Black & Decker tools, they've gone too damn cheap. Overcharging also lights LiPoly batteries on fire, so if you don't have a smart balance charge system with that battery chemistry, you'll eventually pay for the cheapness. Jan 19 '13 at 19:32

I have found the original instructions on this page.

After approx. 3 hours of charging, the battery will be sufficiently charged for use in regular applications. After approx. 8-10 hours of charging, the battery will be fully charged.

After a few lines, it says:

After normal use, a charging time of 3 hours will provide sufficient power for most applications. However, further charging for up to 6 hours could significantly increase the use time, depending on the battery and charging conditions.

  • I have the EPC 18 volt and my instructions says the same, up to 8- 10 hours the battery will be fully charged.
    – user30174
    Dec 30 '14 at 18:35

From the manual... Instructions for jack plug chargers:

  1. Place the battery pack into the tool until it “clicks” into place.
  2. Insert the charger plug into the connector as shown in figure B.
  3. Plug the charger (6) into any standard 120 Volt 60 Hz electrical outlet and let the battery pack charge initially for 12 hours. After the initial charge, under normal usage, your power pack should be fully charged in 6 to 12 hours.
  • 3
    If you found the instructions online, a link to it as part of your answer would be most welcome.
    – wallyk
    Jan 16 '15 at 19:40

If the battery is fully discharged, the formula is: Time(t) = Battery Capacity(q) / Charging Current(i) Units can be hours, amp hours and amps or seconds, coulumbs and amps

For Example, If The battery your charging is 1Ah and the charger output is 100mA(0.100 amps), charge for 10 hours. If the same battery is charged with a supplied charger output of 250mA(0.250 amps), charge for 4 hours.

These equations assume a charger efficiency of 100% which is impossible in real life, charge times may be longer depending on charger efficiency...

  • 1
    You seem to have confused mA and mAh and have assumed a charging efficiency of 100%.
    – Chenmunka
    May 31 '16 at 17:48

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