I believe someone here mentioned that McLaren would use their own ERS, here are Boullier's comments
When asked if McLaren would continue to push this season with work for a "different car" required for Honda next year, Boullier said: "Yes, but if you remember the regulations, the pick-up points are the same for chassis and gearbox. We are developing the car and we are going to keep developing the car for a long time, actually. Most of the upgrades from this car will be carried over to next year's car so that's why we are using this car as a laboratory for next year."
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When it was put to Boullier that his earlier answer meant McLaren would retain its current battery and Energy Recovery System (ERS) layouts will be similar to this year, he replied: "No, it doesn't mean anything like this. To finish the other question, at Spa we have a significant upgrade and another one in Singapore."