When the sides or top of the battery puff you will know as they will bulge out even or past the white plastic and they feal soggy. A liittle bulge is from charging and discharging ( standard use) but puffing out you'll know and the assistant will show a BIG difference in cells.

roy@mcscomputer Posted at 2015-7-20 17:15
When the sides or top of the battery puff you will know as they will bulge out even or past the whit ...

Roy is correct.
Some of you are worrying too much.

The batteries will bulge "slightly" from the heat and gasses generated during charging and discharging.

I always recommend you charge batteries SLOWLY.  Fast charging will shorten the life of most batteries due to heat.

Remember kids, when it comes to batteries, heat kills.  Fast charging = heat.