Quote Originally Posted by mmandley View Post
Thats exactly what it does bro. Its just a right now meter so you can check on your batteries. When the read out is getting in the low 11V range you know you need to consider charging as if it gets to 10.2 the amps power off. You will also be taxing your Alternator really bad.
In reading the owner's manual that came with my SPP2150 (the larger of the 2 batteries): This info is straight out of the manual.

12.85 Volts = 100% charge
12.5 Volts = 75% charge
12.2 Volts = 50% charge
11.9 Volts = 25% charge
11.6 Volts = 0%

John told me that it has been his experience that if you discharge one of these Stingers below the 25% level, then chances are that you have just ruined your battery. After this deep discharge, it will not hold a charge again. I don't plan to discharge mine below 12 Volts, and I plan to put them on the stinger chargers after each trip to the lake. They are on the charger right now.