AEMC Instruments 2140.19 Battery - Replacement 9.6V NiMH Rechargeable for Models 3945/3945-B, 6550, 6555, 8333, 8335, 8336, 8435, 8436, OX 71XX series, & C.A 6116 (Note that 2 batteries are required for Models 6550 & 6555)