For the Parkside 12V cordless polisher/sander (the 75 mm model), there is little practical difference between using a PAPK 12 A3 and a PAPK 12 A4 battery. Both are 12 V, 2 Ah X12V Team batteries and are fully compatible with the tool.
The polisher/sander was originally supplied with a 12 V 2 Ah battery and Lidl specifically lists a 2 Ah battery as the recommended size.
If you do a lot of polishing, the bigger upgrade is not A3 vs A4, but moving to a 4 Ah battery (such as the B-series) if you can find one. A larger battery won’t make the tool more powerful, but it will generally give longer runtime between charges. The X12V Team system is designed so all compatible batteries fit all X12V Team tools.
For your polisher/sander specifically:
- PAPK 12 A3 → 2 Ah, fully compatible.
- PAPK 12 A4 → 2 Ah, fully compatible.
- Performance difference → essentially none.
- Runtime difference → essentially none.
- A4 is simply a newer revision of the same battery.