You measured 12.18V this morning but I am not sure when you last charged it. If it was fully charged recently and hasn't been loaded then 12.18V is very low, it should be approaching 13V. Google 'battery university lead acid state of charge' and look at the graph. Even though your battery is only 2 years old if it has spent a long time below 90% state of charge it may have sulphated and despite what you read on the internet I don't think significant sulphation of a lead acid battery is reversible. I think if you carry on using it it will let you down. When my dad was still driving in his 70s and 80s he used to ask me to fit a new battery on his Rover 45 when it was 3 years old even if it tested OK. He said he would rather pay a bit more than be stuck somewhere away from home in the dark and the rain. I could see his point.
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