Could be due to a couple of issues. First, is the battery low on power? Turn the lights on and run the starter. If the lights flicker as the starter clicks, the battery may need charging or the battery may need replacing. Or the battery cables may be corroded or loose. Check both ends of the battery cables. The positive connects at the starter, and the negative connects on a ground on the engine. Tighten any loose cable connections. If corrosion is present, it can restrict power going back into the battery. Buy some spray on battery cleaner at an auto parts store or Walmart Auto Care center. It will spray on and eat through the corrosion. Also get a battery terminal brush to clean the terminal ends and battery posts when reassembling. The cleaner the terminals and posts are, the better able the charging system can recharge your battery. Remember that every time you start the engine, the charging system takes 20 minutes of charging time to restore the power back into the battery it expended starting the engine. If you make a lot of short trips, the battery may not be fully charged . Each time it's started further reduces the remaining power in the battery. Eventually the battery's power is expended and it needs to be recharged. Being discharged continually will shorten the batteries life.
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