Vintage transistor radios frequently need 9 Volt batteries called PP9. Not the little PP3 ones that are now commonplace. Unfortunately it's very difficult to find anywhere to buy a PP9 battery and even then they are very expensive.

The economical solution is to make one's own substitute, preferably rechargeable. Whatever you construct should be a close match for the size and shape of an original PP9 so that it fits in the radio without falling around when the radio is moved.

In this project I used a battery holder for 8 AA batteries (2x4 configuration with wires attached). The nominal voltage of a NiMH rechargeable is 1.2 volts so the total voltage is 8x1.2 making 9.6 Volts. When fully charged it's little higher and when near depleted it's a little lower. Your radio should work just fine.

If you prefer to use non-rechargeable AA batteries, get a holder for 6 batteries since they are each higher voltage than NiMH cells.

In theory you could charge the finished pack by applying about 11 volts, but it's better to remove the AA batteries and charge them in a regular battery charger so as to ensure they are neither over or under charged.

A set of AA batteries like this holds about half the energy of an original PP9 battery, but that will still operate your radio for many hours – and you can recharge it.

Assembly:

The case has two tiny holes to mark the location for feeding the wires to the PP9 clips. I obtained some old clips and after soldering to the wires, I glued them in place. Remember that the positive wire (red) goes to the round terminal and the negative (black) goes to the castellated terminal.

If you cannot find some old PP9 terminals, there's a small slot where the retaining bar goes so that you can feed the wires out for some other kind of connector.

Creality

Ender-3 S1 Pro

No

No

0.2mm

solid

The base and walls of the case are 1.6mm thick so I set the slicer to walls and bottom of 1.2mm so that they are are solid. I printed without support because the gaps are small.

Filament: PLA or PETG
Walls: 1.2mm
Top/bottom: 1.2mm
Infill: irrelevant
Support: No