Just head over to eBay and look for an extended Mugen battery. I bought one for my 6800 awhile ago and it saved me alot of headache.
The battery WILL last all day (if you use it all day) and it'll last a week or so if you use it sparingly.
http://cgi.ebay.com/MUGEN-3600mAh-EX...item41447b2ffd
Worth every darn penny. I've had mine for over a year now and I abuse the heck out of it.