Using the latest technology, the i4 intelligently select the most appropriate charging current based on automatic battery capacity detection, and when two batteries are being charged at the same time and one of them completes charging, all charging power will automatically transfer to the other slot and charge the battery at the fastest speed. The new i4 is compatible with many more batteries than before and it is easy to charge voltage in each slot independently. The i4 also features many safety measures, including: Optimisation for IMR charging by monitoring the voltage stays within safe limits Overtime charging protection, limiting to 20 hours Made from fire retardant, flame resistant materials Automatic Intelligent Temperature Control preventing overheating Specification Input: AC 100~240V 50/60Hz 0.25A (max) 10W Input: DC 9~12V 1A Dimensions: 140 mm x 94.8 mm x 37 mm Weight: 202 g This item does not include any batteries. UK Plug is included with this charger. Compatible with 18650, 21700 or 20700 Batteries Having fresh batteries to hand is one of the best ways to get the most out of your vape device, and the new i4 charger from Nitecore is among the most reliable and feature-packed chargers on the market. Improving upon the original model, the charger offers a host of new features: 100% Charging Acceleration Active Current Distribution Technology Expanded Compatibility to Support 3.7V and 4.35V batteries IMR Battery Restoration Automatic Current Selection Based on Battery Capacity Automatic Detection of Non-Rechargeable Lithium Batteries 100% Charging acceleration means the NEW i4 can charge at up to 1000mA current in one slot.