If your battery allows you to check the electrolyte level, watch out for gassing and/or a drop in the liquid level in the cells. 8 volts will result in pretty rapid water loss. I'd be more comfortable with a maximum of 7.5 volts at fast idle against a fully-charged battery.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!