its a volt meter. if it goes to high (say around 18 or 20) you risk damaging circuitry. and the number of gauges really depends on the vehicle and the make. some will put as much as they can on the dash
It depends on your vehicle and the trim level that you have. For example a Ford F-150 XLT will have a more comprehensive gauge package than an F-150 XL. The gauge you're asking about is the charge/volt gauge showing whether the battery is discharging or being charged.
