Hacker Sovereign II RP25

[Mike Watterson]

Rechargeable Lithium cells without a shut off / charge controller are a fire risk. This is not a good application for the 18650.

The end point of a 9V pack is about 5.4V to 6.6V depending on the design of the gear (0.9V to 1.1V per cell). So two rechargeable lithium cells of any kind will be fine (maybe 3.5V flat to 4.2V fully charged) assuming you know what you are doing. You'd want a fuse in each pack.

[Murphyv310]

Disagree Michael.
Use the 18650 cells with the inbuilt protection, they cut off at around 3v and wont allow a charge when the battery reaches either 4.3 or 4.4v, none of the flat tops have the protection the pip tops do in most cases, just buy ones that have them, which should be stated in the description.
Here is one site that sells them, loads out there
https://www.ecoluxshopdirect.co.uk/by-si...-protected

[Mike Watterson]

Disagree Michael.
Use the 18650 cells with the inbuilt protection.

Those then are not actual 18650 cells.