New batteries.

OK its these.

http://www.maplin.co.uk/p/maplin-nimh-extra-high-capacity-rechargeable-2400mah-aa-batteries-4-pack-n05bw

My older NiMh charger (maplins) did not like them.

Q and A indicates 1.2 V.
My newish digital battery gauge is confused and 24 hr off charge i measure 1.4V.

Considering they have had some load i suspect they may be hybrid wrongly labelled as NiMh