hot weather and batterys ?

ok this might seem daft but could hot weather affect the car battery ? reason i ask is earlier this week my campaign wouldn't start flat battery . just been to go out in my green mk1 and that's got a flat battery too ! both are used regular each week and nothing has been left  switched on .

Time to get a new battery methinks. GSF do a quality battery at a very affordable price.

the battery on my campaign is only 2 months from gsf and the one on my green golf is only 1 year old. is it just coincidence ???