The EY78A1 uses with a unique 4-pin configuration (+, -, T, ID).
Buy two broken EY78A units (one for motor/gears, one for switch/electronics) and build one working tool. Use an aftermarket 15.6V battery rebuild service (e.g., “Battery Rebuild” on eBay – they replace Li-ion cells inside EY9205 case). panasonic ey78a1 parts
If you only do one repair, make it the brushes. Here’s how: The EY78A1 uses with a unique 4-pin configuration