OK, this is not about a bike but I think it still is relevant to motorcycles. lately, I've been noticing my jeep has been slow to crank. I plugged my Garmin GPS into an accessory socket and the voltage shows between 12.7v and 13.0v at cruising rpm, and down to almost 12.5v at idle this is with air conditioner and radio on. if I turn these off, it will climb to almost 13.2v when accelerating. I assume this is not enough, correct? what is happening - bad voltage regulator, alternator, hamster not running around in the cage fast enough?