Study of OEM and aftermarket IRobot batteries, (R3 and above excluding the IRobot Li-ion).
OEM batteries use a very good cell, typically tests to > 3 .3Ah new @ 50mA/14.4V. The new Blue E-Life > 3.4Ah.
I can't find a reputable battery manufacturer that makes a SubC Ni-MH above a 3.3Ah or Ni-Cad above 2.5Ah, So I doubt there is such an animal.
Testing of the OEM thermistor revealed that the thermistor is +2 to -0 deg. across the charging temperature range. These thermistors aren't the $1.29 +-5 dog. +-5%. They appear to be +2 to -0 +-0.1%, $15 to $20 range if bought individually.
Testing of the aftermarket thermistors revealed many were the $1.29 thermistors. I now know why the aftermarket batteries don't last long and vent acidic fumes causing the green high resistance shorts in the charging detection circuit, CE3. I will still use aftermarket batteries but from now on will replace the T with an OEM. Don't throw those OEM thermistors out, reuse them! If you spent a lot of $ on a Robotic Vac and don't want to mess with replacing the T, buy the OEM batteries and keep your vacuum PCA performing well.
Aftermarket Li-Ion: Reference read first: http://electronicdesign.com/boards/keep-eye-temperature-trends-during-li-ion-battery-charge-and-discharge-cycleshttp://www.robotreviews.com/chat/viewtopic.php?f=1&t=2757
Battery Balance/Protection Board = BatPTB
All of the Li-Ion packs I've tested and tore apart have had no over/under temperature detection circuit, one did have an 80C fuse link. They utilize a resistance indicating to the robot <35C. The resistance changes when charging is complete indicating >50C fooling the robot into high temp no charging mode. Running a home built pack using the above method caused the battery to charge well above the 40C recommended max charging temperature of the cells I used. I now have redesigned my "SMART" circuit to take advantage of a thermistor whose circuit is in the specified charging temperature range and also does not automatically shut off charging when BatPTB stops charge. It will emulate the dT/dt at a specified charged voltage before the BatPTB shuts down charging, Trickle Mode for the final charge to the batteries.
Conclusion: Unless you're prepared to test your aftermarket battery for adherence to quality standards, you should only use an OEM battery. DONT BUY NI-CADS!
Specifics and testing procedures are IP and will not be disclosed. I also like the IRobot Corps. and I'm sure they don't want their IP revealed.
Not all brands tested.