Red Bull team chief Christian Horner admits their latest alternator failure, suffered by Australian Mark Webber, in Sunday's United States Grand Prix is a worry ahead of the drivers' title showdown in Brazil next weekend.
Webber's alternator failure was the team's third this season and came in the race in which they celebrated clinching a third consecutive constructors' championship.
Webber was forced to retire from third place on lap 17 and the disappointment not only put a damper on their celebrations in Texas, but also forced Renault to announce on Monday that they will supply their latest specificiation alternator for the Interlagos race.
"It is just a worry, full stop," said Horner. "Unfortunately it is the third alternator (failure in a race) that we have had, and obviously there have been other failures in other cars. We need to get it back to look in to it.
"I think the new version has raced on other engine cycles (at other teams), so hopefully that is what we will have for Brazil."
Renault's head of trackside operations Remi Taffin explained their plans for Brazil.
He said: "It is very simple. We go for the new spec. It has passed all the tests."
On Sunday, at the Circuit of the Americas, Red Bull elected not to use the newer specification, which was raced by other Renault-powered teams, because it felt safer using the older specification.
Asked why that decision had been made if the newer units had passed all reliability tests, Taffin said: "Because they are human beings and at some point as humans they have some feelings.
"It was a common decision, so we put everything on the table and we decided altogether we should go that way. We had everything to fit either the old or new design.
"But the feeling was generally that there is some sense to keep on using something that we have known for years with low mileage and stuff like that, even if we had a new solution that we knew had gone through all the tests.
"Maybe it is a bit more difficult to understand, but put yourself in the situation where you have to make a decision. Sometimes you go into a shop and there are two different things and your head says you should buy this one but your heart says you should buy the other one."
Defending champion German Sebastian Vettel, who holds a 13-point lead in this year's title race ahead of fellow two-time champion Spaniard Fernando Alonso of Ferrari ahead of this week's showdown, retired from the lead of the European Grand Prix in Valencia with an alternator failure and had repeat failures at the Italian Grand Prix during practice and in the race.
It was after Monza that Renault reverted the team back to older specification parts that had proved to be trouble-free while it worked on updates.