Amiga to 1084 video cables aren't impossible to find. But if he can find one even better.
Originally A2000s came out with a NiCad rechargeable battery which was (prone) to leaking. You'd be very lucky to find one now that still has an original battery that hasn't leaked. If the battery has been removed and there is no PERManent damage you're in good order. The question to ask is "Is the battery still present and is there any battery damage to the motherboard." The machine will run fine without a battery. It just won't keep time/date. Other than that if he is going to open it up to check he may as well advise the Revision number of the MB. V6.1, 6.2 or 6.5 had the least quirks.
http://amiga.resource.cx/mod/a2000.html