18560 3,400mAh Li-Ion Touch 1K Spare Battery
This 18650 battery is a highly tested battery that is protected to prevent from problems caused when short circuiting li-ion batteries. This is the same battery that is currently supplied with the Touch 1K but with the addition of a protection circuit that act like a circuit breaker in your house that prevents too much power being dumped at a time that can damage the battery or even fire.
This battery is a safer option to adding power to you everyday needs to the Touch 1K
NOTE: The Touch 1K is glued shut and to use this battery the seal will need to be broken. There is a blog post that talks about some of the techniques used to do this.