Reading all these posts here, I want to share my real experience with overcharging (may be) with Samsung Galaxy Y ( 700mA 5V USB Charger).
My original battery swell to nearly 2 times its width suddenly in a fortnight, and back went to nearly 10% of original earlier it was nearly 80 - 90% of the original before a month.
I used to plug car charger 5.5V,other chargers and laptop charging also ocasionally, and used to keep charging overnight 50% of the times.
I dont know why my original batt. lived out in just 1.5 years of purchase of mob. in which I guess I charge atmost once a day. So, this hardly equals 500 charge discharge cycle. Original batt, should give near about 800-1000 charge discharge cycle.
When I gone to buy original batt. from a Samsung (only) Retail shop, retailer opened the back cover to mount/check new batt.
Just after opening and seeing the cond. of my old batt. he said the line "Do you used to charge the phone overnight."
I said ,yes. He said it is deduced from the batt.
And, he strongly recommended not to charge overnight/overcharge the new batt.Your old batt. lived out due to overcharging. Usually Original batteries run for more than 2 years.
I asked him,"but the phone has internal circuitry to protect overcharging, and phone shuts down charging once batt has full charged." He said no whatever may be the reason but today phones are not coming with good battery monitoring circuits and they are getting damaged to overcharging, and in the long run batt is gets ruined.
Thats it,
I am also a Electrical and Electronics Engg. I know there are circuits just below the battery connectors on a battery width sized pcb ( I once opened it),
It has temperature sensor (generally on the middle pin which varies voltage linearly with temperature ), short circuit protection circuit ( as batt opens when more than the set level of current flows through it), over discharge protection ( you will get zero voltage on the terminal if pot. diff. of batt. goes below 3V ) and overcharge protection ( may be charging stops or trickle charging start after batt has reached 4.2V , I have not tested it yet but now I will as this happened to me).
By googling around I have read that li-ion batt. swell due to overcharging.
I think most people here who are saying very confidently that batt. are overcharged protected don't have any authentic proof.
But, ya I do agree that costly phones ( more than 200$ ) do have protections as good companies don't skip these small circuitry.
But cheap phones/companies may have cheap circuitry or no overcharge circuitry to cut down the production cost .
Mine is Galaxy Y (less than 150$) ,may be I have burnt out overcharge pro. circuit by using 5.5V charger.
So, whatever may be the reason, its good idea to abandon your habbit of charging overnight or reduce its frequency if you can't.
Otherwise if you are comfortable spending 10$ more in a year, its really not a big deal to bother that much.
so i left it charging for almost 8 hours. the manual indicated "do not over charge for a week" .
