How Did a Protected Li-Ion Battery Reach 4.9V in 4S Series Charging With 19V Supply?

Ok, i know you guys are going to laugh at me for even attmpting to do this, but here goes:

i purchased this battery. from a us-based vendor.

http://r.ebay.com/TNTDiK

i checked the battery voltages on delivery. All were about 3.7 volts. Good sign.

i peeled away the base of one of the batteries, and indeed there was a little circuit board, with a conductor running up the side of the battery to the top.

i connected FOUR of these batteries in series. They gave 15.7 volts.

then i connected a 19 volt wall wart to the ends. after 15 minutes the batteries were warm, not hot. i disconnected, and the pack gave over 17 volts! That's too high-- a 4-pack should max at 16.8 V.

i checked each battery-- 3 batteries were under 4.2 V, but one battery measured 4.9 volts!

How could a protected battery charge to 4.9 V?

thx

I think you will find this site very useful:
batteryuniversity.com

yes, it's a useful site.

The battery university forum is more likely to be helpful, as your question may need the attention of an electrochemist rather than an electrical/electronic engineer, who most of whom will just use batteries.

As a mere technician, I would guess that Li-Ion cell can be charged to higher than nominal voltages, but the protection circuit should normally keep the voltage within a safe range that will prolong the batteriy's life. So the answer to your enquiry may be: a faulty protection PCB.