Air carrier Maintenance Stock Clerk reported shipping Maintenance tools which were returned to be properly configured as Hazmat shipment. Shipment was properly configured and shipped.

Narrative

I arrived to my shift and found tools left over from completed work. These tools were shipped back to their station in which they came from. the tool in question was a laptop that was still sealed from the previous shipment. both tools that I shipped back to their stations were in Pelican cases. I processed the tools and sent them back via COMAT. On my next day while on shift I came across a tool along with old shipping documentation that was the same Manufacturer Part Number (MPN) as the one I had shipped the day before. while looking at it to determine why we were sent a duplicate tool I realized that it posed a hazard and was considered dangerous good. This tool contains lithium battery I was not aware that this tool contain any Dangerous goods. I had never shipped a laptop before and did not think to double check Hazmat because of the case it was stored in. The tool being stored in a pelican case made me believe it was shipped in this case and it did not contain any Hazard markings. Since this tool did not appear to have been opened it still had the locking ties from shipping from what I believe is the original seal from when it was shipped to our station. I shipped both tools in their storage cases only; because this was the way I believed they were shipped to us. The second tool shipped at the same time was in the same type of case with shipping labels affixed directly to the case; so I believed that both of them were shipped in that condition. I did not think to cross reference a laptop as being hazardous. This may have been due to my lack of awareness in shipping this particular type of tool.