Dyson V8 had had new battery and new brushheadhead

The light will have absolutely no effect on the battery life. Your problem could be a caused by a number of things. 1. If you bought your battery from Amazon, Alibaba, or another mail order place, it could be sub standard. These places have no quality control and it's a good place for Chinese manufacturers to unload their sub standard stuff. 2. The Dyson has a sensor that shuts the device off if there is a problem such as overheating. 3.The filter at the top of your motorhead could be clogged. You may not realize that it is because it is very hard to detect. Soak the filter overnight in water, then in the morning shake it under water vigorously to remove dirt. Then rinse and dry. 3 check your vacuum for clogs. I found one in the motor head which was not visible until I disassembled the head.