Given a passage and a query based on the passage, generate an unambiguous, concise and simple answer to the query from information in the passage. Note that the answer may not be present in exact form.
Q: Don't charge a frozen battery. Allow the battery to warm to above 32°F (0°C) before charging. 5. If applicable, remove the vent caps and check the battery's water level and, if low, add distilled water to cover the tops of the plates. How long do you have to run a car engine to charge the battery back to the point it was at before starting the car? Do NOT charge the battery before you test the open circuit voltage. If the voltmeter shows a voltage reading of 12.2 volts then the battery is approximately 50% charged. Since the battery is 50% charged, this means that there is approximately half of the 60 amp-hours in the battery or 30 amp-hours. Slow, fast, and faster: Where to charge electric cars Charging an electric car is not quite as easy as just plugging it in. There are different charging options that fill a car's battery and different rates. In manual testing with the 12V car voltmeter, it does appear that I have about 14,1V to 14,3V at idle with everything off for a few minutes after starting the car, but if I do turn both seats and the AC on, then it goes down to maybe as low as 13,1V or so. The J1772 plug was specifically designed for electric car charging. Problem is, given a typical electric car like the Nissan Leaf, it can take 15 hours to charge the battery from empty to its EPA-rated 75-mile range from that standard household source. Most plug-in cars have a J1772 port, letting them plug into public charging stations. Therefore it is necessary to put about 30 amp hours plus 20% more to compensate for the internal resistance in the battery for a total of 30 amps x 0.2 = 36 amp-hours to fully charge your battery. Step 3: If you charge your battery at a 10-amp rate and you need to replace 36 amp-hours in the battery. To determine how long (in hours) you will need to charge your battery, divided 36 by 10 = 3.6 or 3.6 hours to recharge your battery. A 12 volt / 10 amp 3-stage automatic charger is the best ... Step up to twin chargers on the car and connect to a 240-volt, high-power wall charger (an extra-cost charging unit, not just a 240-volt line) and the charging speed zooms to 62 miles of range per hour, and the total charging time drops to under 4 hours, 45 minutes. If we were recharging the battery with a 15-amp battery charger, the recharge time would be roughly 3.6-hours. Again, this example does not take into account the multi-step charging approach of most smart battery chargers, but it does serve as an excellent guide to battery recharge times. Charge time for a dead battery can take up to 12 hours or longer. There are many factors that determine how long the charge will take, including the size and age of the... Charge time for a dead battery can take up to 12 hours or longer. Query: how long does a fast charge on a car battery take
A: 
It takes 15 hours to charge on a car battery.