Solution:
It could be the alternator not putting out any juice. It could be to blame but the regulator is more likely if it's an internal regulator there not that hard to change
Carrying a set of jumper cables can help you help a fellow motorist—or the other way around. How to jump start a car is usually pretty simple, but it is serious business and you have to do it right to do it safely. Every year people are seriously injured while attempting to help another driver with a “jump.” Clip this how to jump a car battery article and put it in your glove box. Then, before you even connect the cables, go through these steps for how to jump a car battery safely:
Make sure both batteries are the same voltage (most batteries are 12 volts) and the same polarity (both have a negative ground). You can check this information, to know how to jump a car battery, in your owner’s manual in your glove box.
Pull your cars close enough to each other to connect the cables, but never let the vehicles touch. This could cause a short.
Shut off the ignition switch, lights and accessories in both cars. Be sure the vehicles are in park or neutral and that the parking brake is set. Wear safety glasses.
Don’t smoke. Sparks near a battery can cause an explosion.
If the weak battery is frozen, don’t try to jump it! It could explode. You can tell if it’s frozen by looking through the inspection cap to see if the water is frozen. One or more sides of the battery case will bulge if it’s frozen.
Make sure you can identify the positive and negative terminals of both batteries. Also be sure you’ll have enough room to clamp to the cable terminals. The positive terminal is most likely connected to the car’s starting/charging system with a red cable that has a plus sign. The negative is connected to the engine of the vehicle and usually has a minus sign.