The first Joye eGo's were regulated to 3.4Volts. (thanks Scottbee). A bit later the Rivas also regulated came out with "SE Rivas" (special edition) that were unregulated - regular 3.7volt batt curve - 4.1-4.2v off charger, quickly going to @3.7V , then at the end trailing off to 3.2V before needing recharging. The KGO came a bit later and was also unregulated but only sold in the longer 1100mAh batt.
The Joye eGo-c 'upgrade' batt has the best short and charge protection in this style of battery. It also has 2 modes - one constant regulated at 3.4V and the 'vv' mode (not true vv like the Twist) unregulated, just like the KGO and the SE Rivas and other 3.7v unregulated batts.
Both the KGO and the eGo-c upgrade have the 5 click on/off, rated at 10 second cutoff (but the eGo is closer to 12-14 seconds). The eGo-c upgrade has a changing led button - white at full charge, changing to light blue to dark blue as the charge runs out - I find this extremely helpful when heading out - making sure I have two 'whites' and I don't run out of charge. The eGo from the eGo-t and eGo-c's have had three sizes - 650, 900 and 1000mAh. The KGO has added a 650 size, but probably hurt their sales by not having it earlier.
I've had dozens of Joye eGo's over the years and most last more than a year. I fried two earlier eGo's (their short and charge protection has been upgraded since with the eGo-t and the eGo-c at the top) by using a coil that had dropped below 1.3 ohms. Neither the eGo or the KGO are good for 'sub-ohm' vaping, and I rarely have a coil below 1.7ohms on the eGo's.
Both now have knockoffs and clones that genuine batts tend to last longer and have less problems with shorts, threading, etc. During the last four years I've tried a few - Visions, Rivas, others and kept having such good luck with Joye eGo's to where that's all I buy now - mainly the better short/charge protection and 2 mode eGo-c upgrades.