Bizarre Electrical Issue

[gman]

Can anyone help with the following please.....

My 2014 EC300 racing (e start) started bogging down in the woods today and giving it a hand full didn't clear it. I changed the plug with no effect so I put it down to crap in the carb. At this point I noticed the digi trip display wasn't lighting and the e start was flat (20 mins earlier it was perfect). I got the bike home, stripped the carb and cleaned it and the air box, put in a clean air filter and started the bike and it still ran rough.

So here's the odd bit...............

I then pulled the plug, shorted it to the engine, cranked the bike using the kickstart and the spark got weaker and weaker until nothing. I waited 5 minutes, and it did the same - strong spark to start until nothing (died after about 5 "cranks"). Next time I waited 20 minutes and cranked the bike over about 20 times this time until the spark went again (it would appear the battery gathered a bit of charge as the digi trip lit up after waiting 20 mins). I checked the battery and its down to 4 volts so it clearly isn't charging but I don't understand why my spark is "fading" - if the kick start is the back up in the event of a flat battery why am I getting a spark only for it to fade until it dies completely?

I know that a duff battery can cause a bike to run rough but any ideas anyone? Battery or something else?