Jc H the very first thing you want to do is to replace the battery. A failed battery (no longer holding a full charge and/or supplying full amperage) could cause symptoms like you describe.
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=== Update (12/26/2017) ===
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Jc H if this is still the original battery, it is absolutely possible that it is failing. This does happen from one day to the next. If nothing else, a new battery will give you a known-well starting point.
Jc H the very first thing you want to do is to replace the battery. A failed battery (no longer holding a full charge and/or supplying full amperage) could cause symptoms like you describe.