Send the Mrs to the corner shop for some AA's
But seriously - that battery has had to be replaced several times, I have known car batteries last a long time - my VW Polo is 15 years old now! but you are very lucky if you can get 5 years or more out of a bike one!
Raid the piggy bank and buy a battery optimiser, keep it on charge permanently and you should be fine. .3 of a volt drop is nothing.
Batteries are relatively cheap anyway and with your money you should buy one but the rest of us would try to make it last another winter at least.