I'm guess here that you have had the unit for some time? If you leave it plugged in all the time you can actually damage the batteries. Any battery powered (rechargable) device should have the batteries drained periodically to condition them to last longer. My guess is the battery is not holding a charge properly and giving spikes. You can take to battery store and have it checked or if you have a ohm meter you can check for yourself.
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I'm guess here that you have had the unit for some time? If you leave it plugged in all the time you can actually damage the batteries. Any battery powered (rechargable) device should have the batteries drained periodically to condition them to last longer. My guess is the battery is not holding a charge properly and giving spikes. You can take to battery store and have it checked or if you have a ohm meter you can check for yourself.