3.7 volts, mAh stands for milliamps per hour,a measure of how long the batt should last. volts are a measure of how much power they put out at once.
Actually it is milli-amp-hours, not milli-amps/hour.
Also, while the 510 reg batts are 3.7V, the atty is running at only 3.1V, based on Scottbee's electronic explorations. The 14500 batt is also 3.7V, but the atty is actually running close to that voltage.
The 510 PT if it is a straight-wire, no batt box, is running the atty at 5V. But most of them are with batt box and so are running at 3.7V or less, off of a 10400 battery.
I personally am going for 3.7V with higher wattage with a Bartleby. Should be getting here any day now. I want to try this before going to higher voltage so Death-of-attys doesn't come knocking at the door as often, as I think I would mercilessly abuse my attys at 5 or 6V. Also not convinced yet that significant chemistry doesn't happen with higher voltage, as I've not seen any vapor tests at higher voltage...maybe someone can point me to any reports here. TIA!