The MH-26aAK is an Adapter Kit for use in charging or calibrating the EN-EL4/EN-EL4a Li-ion batteries on the MH-26a battery charger. The MH-26a battery charger can be used to charge and calibrate the EN-EL18/EN-EL18a rechargeable Li-ion batteries that power the D4 and D4S D-SLRs as well as the EN-EL4/EN-EL4a rechargeable Li-ion batteries that power the D3 series D-SLRs. The kit includes one MH-26a battery charger and one BT-A10 Adapter. To charge the EN-EL4/EN-EL4a rechargeable Li-ion batteries, attach the BT-A10 Adapter to the MH-26a. The BTA10 Adapter comes bundled with the MH-26aAK Adapter Kit for the MH-26a.