Bosch 12v Battery Restoration, Replace Old Ni-Cd or Ni-Mh With Li-Ion Cells
by atarico in Workshop > Repair
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Bosch 12v Battery Restoration, Replace Old Ni-Cd or Ni-Mh With Li-Ion Cells
A friend gave me a cordless drill/screwdriver that he was no longer using. He told me that the batteries he bought in the past to replace the original ones didn't last long enough. I saw online that by disassembling the batteries, it is possible to replace the Ni-Mh cells with Li-Ion cells. Since I had the necessary tools, I embarked on the repair adventure. I am very happy with the result! The range has tripled and I can even use the battery for other uses.
Supplies
What to buy
- BMS, a circuit the protect the Li-Ion cells (Link). BMS is an important part of the battery, this reference is just an example and you can buy a better one.
- 6 Li-Ion cells (Link) avoid pre-built pack with a plastic structure, they'll not fit the battery package
- Nickel metal tabs to connect batteries (Link)
- Charger (Link)
- Li-ion Capacity Indicator Board (Link)
- Charger connector (Link)
- Some electric wires, cardboard
- Hot glue stick
Tools
- DIY Arduino Battery Spot Welder Kit (Link) and battery or similar
- Soldering iron and tin
- Hot glue gun
- Screwdriver for torx
- Drill and bits for metal
- Multimeter
- Eyes protection
Note: the Spot Welder with its battery is quite expensive (200$), so ideally try to borrow it.
Tear Down the Original Battery
Unscrew the 4 torx on the battery, one is hidden under a plastic cap.
Pull apart the two elements of the case and remove the plastic clips and metal springs. The Ni-CD battery (each cell is generally wrapped in cardboard) and the connector comes out.
Separate the connector from the battery, cut and remove the temperature sensor (2 thin wires). Put to recycling the battery block.
Prepare the Enclosure
Drill the hole for the charge connector and battery gauge cables. Check the inside of the enclosure for enough room under the connector.
Prepare the Li-Ion Battery Assembly
The cells should be placed in alternance. The second level is arranged the same way as the first.
Hot glue the 6 cells together (hot glue is used since years to build battery assembly and even in the car manufacturing for pcb rework), in a 2x3 pattern. Avoid the plastic supports, they take too much room in the battery enclosure, you'll not be able to close it.
Paste with some 2-sided tape the BMS to the battery, this will guide you to place the tabs.
Clean with alcohol the metallic surfaces of the cells and of the tabs for improve soldering.
Cut the tabs in the correct sizes. Some tabs should be longer to make the contact to the BMS circuit.
Spot Weld
Spot weld the tabs to the cells to make a 2P3S battery. This means that 2 cells are in parallel and then 3 set of them in series.
Wiring
Pass the cables of the battery gauge in the hole. Connect it to the charge connector and add to the connector 2 additional wires that will connect the battery.
Finally, weld the charging cables and the cables to the drill to the BMS (the green board mounted on the battery)
Reassemble
I suggest to glue some cardboard over the conductive parts and add some thin plastic foam to the bottom. Then insert the battery in the enclosure, reassemble the clips and springs, close the enclosure and remount the 4 screws.
Test it shortly in the drill, but charge the battery before star working with it :-)
Charge the Battery
Please be careful, the original Ni-CD/Ni-MH charger is not suited for the Li-Ion batteries. You can send it to the recycling or use the components for another project.
The new charger connects directly to the battery via the cylindrical connector.
With a battery capacity of 6Ah and a charge current of 2A, the charge will take a little more than 3 hours (at the end, the charge current is reduced).
Identify the charger and the charge input on the battery to avoid to use another supply circuit. In fact, the connector used here is used by many power supply with various voltages and functions. This could damage the battery.
I Built a Super Battery, and Now?
The charge connector is reversible, so the battery can be used to power other 12V appliances, like a car phone charger or a 12V lamp, check the picture above for 2 examples.
With this manual information, you can upgrade the battery from other tools, i suggest to check before online if is feasible.