Tiny Mega Charger.

thingiverse

Print out two VP_tube_plug.stl designs and slice a suitable length from a VP plastic tube, perfect for accommodating four AAA batteries. For these cells, you'll need to allow about 225mm of clearance in total. Next, drill a hole through each end, using a diameter of 7.5mm for maximum access. In addition to the plug components themselves, two springs will also be required along with banana connectors. Attach everything securely and link up your chosen charger. Be sure to set it for Nickel Metal Hydride battery chemistry. Since I've got four AAA batteries on hand at 1.2V, 850mAh capacity, I'll have the charger configured like this: NiMH mode at 4.8V charge level and 850mAh amp limit. To cater to eight identical batteries of the same capacity in parallel, adjust the setting up to Nickel Metal Hydride battery chemistry for a charge level of 9.6V and keep the same current limiter at 850mAh – repeat as necessary to match your specific charging needs