This is a battery adapter suitable for Ferrex

The battery's built-in power status monitoring function is quite basic. Therefore, I added a digital voltmeter to my design to continuously monitor the battery voltage and avoid deep discharge. To save power, the voltmeter can be turned off via an internal switch

The B2+ contact on the battery outputs a nominal voltage of +20V, while the B2 contact outputs 0V

The battery of the 40V version consists of two internally independent 20V "half-packs", which are independently connected through two pairs of terminals, B1 and B2. In the 40V version, my adapter only draws power from the B2 half-pack, so the nominal supply voltage is still 20V, and the available capacity is only half of the total capacity of the 40V battery pack.

Note:

• Please note that the safe use of lithium batteries requires professional maintenance and management. If not handled properly, the battery pack may catch fire or even explode. Such safety protection electronic circuits are usually built into the original Ferrex tools and original Ferrex charging adapters. If you use my adapter to power the lithium battery, you need to strictly comply with the corresponding safety measures by yourself.
• It is essential to use the original Ferrex battery charger and strictly follow Ferrex's safety instructions! Never charge the battery with my adapter. Over-current charging, over-charging, discharging the battery to below the minimum voltage threshold
• Drawing excessive current from the battery pack or experiencing a short circuit could potentially cause a fire or explosion! I have no exact understanding of the possible fuse protection mechanism within the battery pack or its maximum allowable current. It is speculated to be around 10A, but this is just a hypothesis. Neither Aldi nor Ferrex's official websites have published relevant maximum current specifications. Moreover, my adapter completely ignores the fact that genuine Ferrex tools might use an intermediate contact
• The battery pack appears to lack a protection mechanism to prevent the battery from discharging below a safe minimum voltage. Such protection is typically built into Ferrex tools, which automatically stop operation once the battery voltage drops below a safe threshold. Therefore, you need to ensure that you stop discharging the battery in time before its voltage falls below the safety threshold. If the battery is discharged below the minimum voltage and then recharged, there is a high risk of fire or explosion. For this reason, the original Ferrex charger may permanently refuse to charge the battery once its voltage drops below the safety threshold.
• When not in use, please be sure to disconnect my adapter from the battery to avoid accidental short circuits.
• If you plan to modify my adapter to use the two half-packs of the 40V battery pack in parallel
• Using my adapter may void the warranty of your Ferrex battery pack.
• Please do not let people who do not understand the above points use the adapter, and children should not be allowed to use it either.

In order for the cable stress elimination device to function as expected, the width of the circular cable groove must closely match the cable diameter

• Download and install OpenSCAD from openscad.org
• Open the .scad file in OpenSCAD
• Adjust the value of the "d_cable" variable according to the diameter of your cable.
• Click on "Design/Render" to render the image
• Click "File/Export" to export
• Import the exported file into the slicing software and print it

The specifications of the sheet metal screws are 2.9×9.5mm

The AMP connector uses a 6.3mm

The voltage meter selected is the XH-028 V4.0 model, which is supplied through the following channels, for example:
https://www.ebay.com/itm/125809771454
https://de.aliexpress.com/item/32828845267.html

It is recommended to apply a drop of hot melt adhesive at the welding point of the voltage meter leads to fix and isolate the red and black voltage meter leads, so as to prevent a short circuit caused by the leads breaking at the welding point.

The baseplate size of the switch is 12×12mm, and the contact spacing is 5.08mm

If you use a different model of voltmeter or switches of different sizes, you need to modify the voltmeter() and pushbutton() modules in the attached .scad file. When rendering, these two modules will be subtracted from the cover plate using OpenSCAD's difference() operation, thereby creating the required openings. Therefore, modifying these two modules will automatically generate an adapted cover plate .stl file. If you want to change the distance between the two mounting holes of the voltmeter

You can find more information about Ferrex battery packs here:
https://www.youtube.com/watch?v=H9Mb5_nCVeo
https://www.youtube.com/watch?v=2d6iggXptNc
https://www.youtube.com/watch?v=jBfbqZHedto
The above video was not made by me.

However, these videos were not created by me, so I cannot take any responsibility for them. I haven't opened my battery pack yet, so I can't confirm or deny anything at this point. Additionally, please note that Ferrex may have replaced the battery cell types in different production batches.

Please also refer to my Bosch 18V battery adapter:
https://www.thingiverse.com/thing:4891096

To-do list:
The next major goal is to integrate flat fuses for automobiles. Maybe one day...