In Electronics/ Manuals Posted by Mark Spencer May 23, 2014
Cordless drill conversion to LiPo power
You are about to finish your project, reaching out for your trusty cordless drill just to find out that the battery is empty, &$*!@!$. We all know this happens just too often. Batteries used in cordless drills are usually of Ni-Cd chemistry which has high self-discharge rate. This means that chemical reaction inside the battery is reducing it's charge without any connection between the electrodes, just by sitting on the shelf. Ni-Cd are especially prone to this losing it's charge pretty quickly. Another problem is that these batteries are usually of low quality with low number of possible charging cycles.
Battery replacement usually costs as much as new drill. Last several years we can see new battery types emerging as standard in Radio Controlled hobby thanks to cheap Chinese production reaching reasonable quality levels with exceptional price.
This particular drill I'm about to modify is powered by 14.4V Ni-Cd. Adequate replacement would be 4S LiPo but 3S will do just fine, especially since I have bunch of Zippy and Turnigy 2200mAh 3S packs lying around unused. These comes for as low as 8$ per pack.
With 11.4V storage charged 3S battery drill is a bit slower but torque is outstanding compared to original Ni-Cd batteries. Have in mind that LiPo batteries don't like being fully charged for too long. Having it sitting for months fully charged will reduce pack's life.
Another, better but pricier option are LiFe batteries. These come with lower than LiPo nominal voltage of 3.3V per cell, and since full Ni-Cd battery cell voltage is 1.5V, original 12-cell pack's maximum voltage is 18V. Maximum voltage of LiFe cell is 3.6V making 5S pack and ideal choice.
Anyway, which every battery you choose this simple modification is the same.
Old Ni-Cd 12 cell battery pack.
Pay attention to the polarity of battery, don't fry your drill.
Dab of hot glue to hold the connectors in place.
I've cut the hole on the case to get the balance lead of the battery out. This way i can charge the battery with my LiPo charger while it's still inside.
Battery will be permanently damaged if voltage drops too low. I'm using cheap LiPo low voltage buzzer connected to the balance lead while using the drill to let me know when the battery is empty.