While a low charge state can be simply avoided by charging the device more often, the battery in the Nexus S by default is charged to around 95% capacity and I could not find any app or tweak to stop the charging at a lower capacity. Thus the only way was to use the manual override and pull the cable which is annoying since one had to monitor the charge state.
So I implemented a simple tweak I called Battery Life eXtender (BLX) which can be used to set a limit for the capacity to which the battery will be charged by passing a value between 0 and 101 to 'charging_limit' in '/sys/class/misc/batterylifeextender' (101 by default).
Changes to the source code: http://www.pastie.org/2516542
The battery status is set to 'full' once the user defined charging limit is reached.
Bug fix: http://www.pastie.org/2534319
The charging limit is set to 96 by default which will mimic the behaviour of the stock kernel. Also, the maximum value accepted by 'charging_limit' is set to 96.
Bug fix: http://www.pastie.org/2560599
1. Made BLX compatible with the 100% charging 'fix'.
2. If the charging limit is set to the maximum charging limit, charging will not be stopped until the interrupt signal is received from the MAX8998 chip.
No further patches will be published here. I have set up a git repo for all my tweaks. Each mod has its own branch to keep the tweaks cleanly separated and one can simply pull the latest patches from the corresponding branch.
I do not accept donations and since I reached my 50GB limit of free space on SpiderOak, thanks to all of you kind people who got an account using my referral link, I could not ask for more.
Instead if you really want to donate your hard earned money to someone who deserves and needs it, consider donating to the Free Software Foundation at fsf.org: These guys are at the frontline when it comes to keeping Linux free and fighting these greedy bastards who think they are entitled to collect royalties and other fees from Linux users due to some silly patents - and if Linux falls, Android will be next.