arr a good old MP5K that's how mine used to look , they are a good gun, abit low on FPS (i only managed 250FPS on a SP100 spring!), but they do have a distinctive sound ... and i have not seen many on the field. (word of warning the standard box is only 6mm, so not the best for upgrades etc)
as for the battery if memory serves me correctly, you need a 8.4v 1300mah stick (don't be tempted by the 1600's ... they wont fit ... or they didn't when i bought one .... best to measure up to be sure though)
as for fore grip unless you can find a TM MP5K kruz fore grip, there isn't a lot of options, as if you fit the ris kit like i did you loose access to the battery-connector/hop adjuster area. and a standard MP5 forgrip is wayyy too long.
That said by looks of it you have also lost your fuse holder and the majority of the mini tamyia connector
When was the gun last serviced?