Battery trouble

Jolly handy this new multimeter! The battery is reading 10.8V or 14.4V when the engine is running, which seems to indicate a battery issue not the alternator. The battery was only put in when the LS3 was added so less than 12 months old – diagnosis is a faulty battery. I can’t rule out something draining it but neither can I afford to not know whether the car will start each time I go to it, so I have purchased an Optima Red Top battery (730CCA) and also a DBPower DJS50 Portable Car Jump Starter. Both arrived this morning & having failed to start the car on the battery I’ve tried the DBPower portable starter & it worked first time – in fact I have to say I am very impressed with it! Small, light, with it’s own hard case & plenty of connectors to power phones, laptops & anything else requiring USB power… A seriously cool piece of kit..