We have approved the LG HE4 and the Samsung 25R. Other 18650 high drain lithium ion batteries will work if they meet the 20A continuous current rating and are rated to discharge down to 2.5 V with a 4.20 V at full charge. For Zion, the batteries should be a matched pair. The batteries will need to always be used together to ensure discharge equilibrium. If old, non-matched batteries are used your Zion it may not function properly.