Ask the ex­pert

Total 911 - - Views - Scott Gard­ner Job ti­tle Gold Di­ag­nos­tic Tech­ni­cian Place of work Porsche Cen­tre Bournemouth, UK Time at Porsche 12 years

Got a ques­tion for our Porsche tech­ni­cian? Email us ed­i­to­[email protected]­ With re­gards to my 996 Turbo, the new bat­tery car­rier and bat­tery are all fit­ted and the car does seem to start bet­ter with an 85ah bat­tery fit­ted rather than the 71ah it came with – I know it should have had at least an 80ah on there, buyer be­ware! So, a quick ques­tion: would a lower power bat­tery have any ef­fect on the way the car runs? Ob­vi­ously the car draws ‘X’ amount of power from it as the en­gine runs, but would it af­fect en­gine per­for­mance or cause is­sues else­where with spark, tim­ing, ig­ni­tion and so on?

Ja­son East

In short, the answer is no. A smaller bat­tery does not af­fect the way the car runs. A car’s bat­tery is mainly for start­ing the en­gine as the starter mo­tor draws a high cur­rent for crank­ing.

The amps and volt­age are reg­u­lated by the al­ter­na­tor to main­tain cor­rect volt­age, not the bat­tery. There­fore, once the en­gine is run­ning, volt­age will be main­tained around 13.5 to 14.5v de­pend­ing on elec­tri­cal load and bat­tery charge sta­tus.

If you think about it, a com­pletely flat bat­tery can still be jump-started and the car will then run fine. As long as the al­ter­na­tor is do­ing its job and reg­u­lat­ing the volt­age then the car will run the same, re­gard­less of bat­tery size. A big­ger bat­tery will mainly as­sist on start­ing your 911 from cold as they will have a higher cold­crank­ing amps ca­pac­ity.

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