Shutdown Timer: Ideal for Cordless Tool Batteries

About: I have worked in agriculture for forty years in south Georgia. If you live your life and never know me, you've lost nothing, but if you live your life and never know Jesus Christ, you've lost EVERYTHING!

I have grown very frustrated over the years with disappointing "rechargability" on cordless tool batteries. It is too easy to become preoccupied with other tasks and overcharge batteries.

I see use for charging batteries for trolling motors or lawnmowers, lots of other times when it would be nice to turn it on set to turn off a set number of hours later.

This Instructable is a pretty simple solution for something that simple minds like mine would not automatically think to do. Professional and Advanced workers have the sense, discipline, and good habits of not overcharging batteries. I don't.

I see the words: CAUTION! Recharging the Battery Pack for more than 5 hours can damage the battery cells in the instructions and plan to remove the battery from the charger, but by the time I shower, eat supper, watch a little TV, I forget to remover the batteries and go to bed.

A "shutdown timer", sometimes known as a "countdown timer", is the solution. It's easy to find decent 24-hour cycle timers for the $6-$15 price range, but I honestly failed to find a shutdown, or countdown timer.  If I set the 24-hour cycle timer to charge for three hours, I have to remember to go back out the next day and remove, and I just might not remember to that.

After some amount of time of searching online shopping at major retailer sites as well as other online retailers, I failed to find anything that fit. I thought about the timers I see in bathrooms for ventilation fans or sunlamps, and was able to find those.

Step 1: Put It Together

So, I went my area Lowe's store and bought:

    12 Hour Spring Wound Countdown Timer (This is one that is typically installed in bathrooms for ventilation fans or sunlamps.)
    4-11/16" Square Receptacle Box (metal ready for 2 gang)
    15A Decorator Receptacle (I liked the square shape)
    Screwless Receptacle Cover (to match the the decorator receptacle above)
    3/8" NM Connector for a strain relief

I already had a 3 prong heavy duty appliance cord.

Total costs came to $29.97, lots cheaper than new batteries.

I wired and assembled the box, found out I had to adapt just a couple of things to mount the receptacle and covers, but was pretty easy.

Now I can put my batteries on charge, set for 3 hours, and go to bed!

EDIT EDIT: I added a backing board to the unit using 1/2 inch plywood. I also added a 120VAC indicator lamp to the outlet cover that comes on when current is flowing. I mounted the drill charger bases by running a  pair of drywall screws through the board from the back into the base of the chargers. I then used a cable tie to bundle the charger base cords, maximizing portability.

I think I am going to put some picture frame wire across the back to so that I can have the option of hanging this thing if I want.

There is a spot at the bottom that would be ideal for a power strip in the future, perhaps.... 



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    7 Discussions


    2 years ago

    hi, good instructable. something that is needed for sure. i also have a lot of rechargables for mower, weedeater, hedge trimmer, and lithiums for small stuff. on ebay, i got an outside lights timer with photo cell as it was 2-4-6 hour shutoff. its heavy duty and easily activated with a small flashlight....with tape covering photo cell till i flip it back to activate. i set it to 2 hours and find thats great for almost anything lithium...and no sound at all. about 15 bucks and tough.


    4 years ago on Step 1

    I have the Shark SV780 hand vac and there in the manual it says 16 hours.


    6 years ago on Introduction

    Excellent idea. I've got several dead batteries that I suspect had early death due to them being on the charger all the time in the garage. Probably being on the charger forever and being subject to temperature changes throughout the hear of +107 to -20. If it's true that the temp fluctuations help kill batteries, I need to make a battery charging cabinet in the house that is dedicated to my garage stuff!

    1 reply

    6 years ago on Introduction

    I like your Idea and it had never occurred to me to use that type of timer for this purpose. I'm planning on going out and building one for my self to use with all of my chargers.
    Keep up the good work

    1 reply

    Reply 6 years ago on Introduction

    Thanks for the encouragement, Dan. May you see your effective battery life on all your tools extended!


    6 years ago on Introduction

    Dumb chargers are pretty bad. I always tell folks that smart chargers are a wise investment. The issue you raise with leaving batteries charging for too long is real.