I am a new FT-817nd owner and its been a very fun radio. I have only had it 2 weeks now and have filled 2 pages in my log book with contacts one in Poland. So 5 watts works fine into my end fed wire.
The included charger will only do that, it says in the manual that the radio must stay off and it will not power it. I found a great power supply and it seems to work very well and the price not all that bad. It meets all the needs of the 817 just fine and will charge the on board battery at the same time your running it.http://www.allelectronics.com/cgi-bin/item/PS-1231/480/12_VDC_3.5_AMP_POWER_SUPPLY_.html
Hope that helps.