I bought a "new ?" 3 amp hour battery for my 12 Volt Makita . It was a dud from the start . Low power probably been sitting on a shelf for 5 years and its not getting better with use .
The replacement had screws to separate the battery , the old did not
Step 1: Get the Old Batteries Out.
So I noticed the old was usable as a Lithium Ion conversion so I
found a convenient place to cut in with a hacksaw and just cut in till the plastic separated. Cut all round then a screwdriver blade separates the halves nicely and it even snaps back into place and stays there afterwards.
Put the old batteries in a vice and twist the plastic housing away from it and the battery breaks out . The top connectors just push out too so there you have a temperature sensor and something else that attaches to the side of the batteries . I left the temp sensor there but the other thing does not seem to affect charging . If anyone knows what it is please comment.
Cut the battery connectors away from the batteries and save .
You need 3 Lithium Ion 18650 batteries which are nominal 3.7 Volts . Don't take below 2.5 Volts nor above 4.2 Volts -A BMS (battery management board ) for 3S (3 in series ) and an old battery case.
Lithium Ion 18650 batteries-Watch out . You want as high a capacity as possible but they all lie . I got some advertised as 100.000 mAh and what i got were about 900mAh.
A BMS (battery management board ) for 3S (3 in series )
But have a search around . You can do better than that
Step 2: Fit the New Lithium Ion Batteries in and Test
I took a sharp chisel and removed the plastic supports all round top and bottom.
I used a protection board I got on ebay for pennies and ran the wires as shown . get it right or it wont work and use the same colours for red and black , Pos and Neg and some other wire for the sense wires . I used green I also used pre-tinned insulated wire from ebay .
Strip the ends and tin first and use a strong powered iron and drop blobs of solder on the ends of each battery. The three batteries are connected in series and the sense wires go to the junctions and the last positive terminal to complete it. Leave it all out and test in the drill and in the charger before you click the case back together. You will probably want to tape or glue the pack back together to stop it falling apart if you drop the drill.
Step 3: Improvements
I'm working on getting this better and it seems that 4 in series produces a better torque and speed as that's giving nominal 3.7 x 4 = 14.8 Volts so the motor runs sweetly at that. Max voltage is then 4 x 4.2 = 16.8V.
Just tried it with 5=21Volts and the motor purrs . These motors are hardy
The charger continues to show a red flashing led so its probably set up to output something like 18 Volts and that device attached to the side of one of the old batteries is probably to stop the charger at some pre-defined voltage. So I will see if this is the case and update this then.
This change to 4 necessitates a 4S version of the BMS and I have some coming so cant leave the pack in the charger too long in case they go out of balance. You can get them here for a few bucks.
The 12 amp should be OK but its little more for the 20 Amp version.