Originally Posted by DGXR
If you are using a suitable viscosity, your engine oil will have zero effect on your battery life. Even if you are not using a suitable viscosity, the small difference in cranking times will have zero effect on your battery. As RDY4WAR noted, only a combination of very low temperatures and a heavier viscosity could ever allow the motor oil to affect battery life... and that would be really severe circumstances. The alternator is designed to recharge the battery after a heavy draw from the starter motor.
Okay thanks i went to check on the alternator and it had some issues plus a new battery installed, now which oil should i go with semi-synthetic or mineral 15w50 instead of 20w50 in winter