The third prong is for a temperature sensor that helps control the charging and it is much safer
DCS Series: DCS331B
0Ah P108 Battery for Ryobi 18V Power Tools
4V Power Tools1 x User Manual
For Makita 18V Battery Replacement | BL1830 6.0Ah Li-ion Battery 8 Pack Chargers & Adapters The third prong is forUp to 50% more run time than BL1830 Replace Original Makita Battery Code: 194205 3, 194309 1, BL1815, BL1830, BL1840, LXT400 Ideal replacement for all past and current 18 volt Makita products. Fit Original Makita Model(Use"Ctrl+F" to find your own PN & Model): BDF453SHE, BDF454Z, BHP452, BML184, BML185, BST221Z, BTDW251Z, ML185, TD140D, TW251D BCS550, BCS550Z, BDA350, BDA350Z, BDF451, BDF451Z, BFR550L, BFR550Z, BFR750, BFR750L, BFR750Z, BFS450,