Megane won't start properly

[figurine]

I've a 2011 Megane and last week I tried to drive it but it wouldn't start. I put the keycard in and the lights etc came on as normal, but when I push the start the engine sort of splutters and the lights on the dash dim and then die briefly before coming back on but the engine doesn't start properly. I think the battery possibly needs replaced, going to try jump starting it tonight to see if that makes a difference, but wanted to see if it could be anything else obvious that I'm missing?

Thanks (apologies if this isn't in the right place)

[GreenV8S]

A flat battery would give those symptoms, so I think your diagnosis is correct.

It may be a knackered battery unable to maintain enough current under these conditions, or a fault on the charging system preventing the battery from charging fully, or a residual current drain which is flattening the battery while it is parked. Or perhaps you just left the lights on.

Even if the battery was not the original cause of the problem, being flattened won't have done it any good.