When i was in grade 5, pokemon red on the gameboy was all the rage on the schoolyard. AA batteries were constantly running out. One day, this one kid showed up with a massive 4S alkaline D-cell battery pack, soldered together and duct-taped to the back of his gameboy; his dad had built it for him. That was the inspiration for this repair/upgrade.
Selling points of this design:
Battery holder fits in the hand while holding the NDS lite.
Can be charged through the charging cable just like the original battery so no need to disassemble for charging.
Parts will interlock for easy assembled but also be sturdy and solid for daily use.
Uses the original screw from the original battery lid.
Uses common, standard parts.
Lasts for 8 hours of gameplay, Sleep mode for for 3-4 days.
Assembly instructions are available on the thingiverse page.
Source code for 3d printed parts are available for Fusion 360.
3D printed parts from PETG
PETG or stronger is ideal due to flexability and strong inter-layer adhesion. PLA may work but not recommended.
PCB protected (against under-voltage) 18650 cell
These are easy to find over amazon, aliexpress, ebay, etc. as high power flashlight batteries. You can also salvage them from laptop battery packs, cheap powerbanks, discarded Teslas, Powerwalls, etc. but salvaged cells must have a under-voltage PCB added. These PCBs can be sourced from aliexpress.
Approx 100 mm total
Flat copper strip, or metal strip
Those plastic/metal anti-theft magnetic sticker markers contain 3 usable strips each!
M2 Screw, 4mm
Longer is not recommended as they will poke into the battery.