Is it normal to have 40% capacity after 1.5 years of charging Li-Ion?
Battery gauges often don't work well with aged batteries, so the state of charge you are reading can be pretty inaccurate.  

Also, the ideal state of charge for long battery lifetime (obviously not runtime)  is around 50% charge.  If you leave it plugged in all of the time at 100% charge you will reduce the useful life of the battery.  

Some laptop manufacturers have a mode that only charges to 50% if you intend to plug it in for long periods.