Intermittent starting problem with 2012 Renault Scenic 1.6

[Klp100]

Problem started last week in the cold. Went out and wouldn't start. I can hear the starter motor click so I jump started it and started fine, was then ok for the rest of the day/the next morning.
The following afternoon it was doing the same thing. We swapped the battery over and all was fine.
Drove around 250 miles on Sunday, and she started fine yesterday.
Started fine this morning but then around 3 hours later, wouldn't start again.

It's a new battery so I can't work out if it's likely to be the alternator? Tried giving the starter motor a couple of hits incase the jump start was a fluke, but nothing.

Any ideas on what this could be?

[littleredrooster]

Alternator is probably goosed. Get the engine started & put a voltmeter across the battery; you should have 13.8-14,2v. Anything less means it’s not charging.

[shakindog]

If it’s the one I think it is.
Check the spade connector on the thin exciter wire that goes on starter motor it’s a common thing on them for it to corrode and either resistance goes up or it starts to break off.
Could be wrong but all it’ll cost is 5mins of your time and a wiggle of the wire see what happens

[E-bmw]

You need to buy/borrow/steal a multimeter & see what the voltage is at the batter with/without the engine running.

A good fully charged battery will read around 12.6 volts, for every 0.1 volt less than that it has lost around 20% charge, so at 12.1 volts it is pretty much flat.

With the engine running & the battery charging you should get over 13.5 volts, but more likely around 14.5.