Cordless Drill With External SLA Battery

The battery on my old drill was going dead way to fast so my solution was to make it work on a SLA battery. I checked and there are a couple of similar instructables but none that have the option to use the original battery which was important to me. Caution: I am not responsible if you ruin your drill

Parts required:

power connectors

wire (16 gauge or lower)

blade connectors 2x

SLA battery

heat shrink tube (optional)

Tools required:

another drill

drill bit (21/64 if using same plug as me)

screw driver

soldering iron


wire stripper (recommended)

hot glue gun (optional)

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Step 1: Disasembly

simple enough, just remove any screws and other parts holding the drill together.

Step 2: Planning

Now is the time to figure out where things will need to go and how to get there

Step 3: Drill and Wiring

This is where it all happens, you will want to drill a hole in the case and then thread in the connector if you you are using the same type as me. It is very important that you get the polarity right, at best the drill wont work but at worst it could probably kill the drill. From there you will need to solder on the wires and if you plan to now is a good time to add some hot glue. I did this to both insulate and reinforce the connection area. After thats all done its a good idea to test it out before reassembly.

Step 4: Final Notes

The drill i used is 14.4v and the SLA is 12v the closer your drill is to the battery voltage the better it will perform. I have no idea what these DC connectors are rated at but i know that the drill can go up to 18 amps! It may or may not last. Also the longer the wire you use the more voltage drop you will get, i went with 10' and you can tell it goes slower so larger wire is recommended. Other things you might want to consider is a car adapter which is easily made also a fuse might be a good idea, if you do use a car cigarette lighter make sure it is rated for at least 20 amp or more.

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    7 Discussions


    3 years ago

    I would like to do this with my old 12v ryobi cordless drill. Do you know if I can use a standard automatic auto/car battery charger that is switchable between 2/10 Amps to charge the SLA battery?

    2 replies

    Reply 3 years ago

    I would recommend against this to avoid any damage from over charging. Even at 2 amps the current is above the limit for a 7AH battery. I use a cheap charger purchased off ebay and have had no problem just search SLA charger. Honestly i no longer used this as i purchased a new drill but if you modify your drill you should try to use a more robust connector as i had issues where it would unplug easily.


    5 years ago

    I had the same idea, although once I found how crude it was, I wanted to try to make it better by using a bldc motor. the brush motors are just trash Imo.

    1 reply

    Reply 5 years ago on Introduction

    I agree, brushless motors are some nice. Someday money permitting i would love to just upgrade to a nice drill, something like a milwaukee or something of the sort but for now this one gets the job done. I cant see myself trying to swap the motor thou lol