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.*The EN-EL18 Li-ion batteries are also used to power the MB-D12 Multi-Power Battery Pack for the D800 series D-SLRs**The EN-EL4/EN-EL4a Li-ion batteries are also used to power the MB-10 Multi-Power Battery Pack for the D2 series, D700, D300 series D-SLRs; and MB-40 Multi-Power High Speed Battery Pack for the F6 SLR