mac book pro battery heats up even when unused.

Hello. This question is about a Mac Book pro, 2.2GHz 2011running OSX10.9.5.It's a refurb, bought 2 months back.

The battery, after about 10 minutes of use, goes under 15% remaining. It then runs down a little more slowly over 20 - 40 minutes, depending on what's running (currently the Activity Monitor says 95% capacity is not being used)

Battery status is given as normal, 42 cycles only so far.

I have downloaded an app called Coconut Battery which says the battery is in good condition, but, even when the mac is hardly being used and powered from the mains, is at around 40degrees C.

I have tried resetting the PRAM and the SMC (twice).

The company that sold me the Mac Book Pro have promised to replace the battery but they're not exactly hurrying....in the meantime I am wondering if there's another reason for this situation, given that all indications are that the battery should be in good condition?