I've noticed the battery life on my 705 seems to have taken a nose-dive, although on occasion it does surprise me - one day, recently, in the car, it seemed to run (for the kids) for a couple of hours (playing video, volume on full). There was definitely a full charge before that.
A few days earlier, though, with full charge, and it only lasted somewhere in the region of 5-15 minutes before shutting itself down.
In general, without mains, even when charged fully before going out, most times the battery life is shockingly short, now (as I said, though, apart from the really occasional anomaly mentioned above).
So I've decided to get a new battery, I've ordered one of these:-http://www.amazon.co.uk/Replacement-Battery-rechargeable-manufacturer-warranty/dp/B002NE8WD8/ref=sr_1_4?ie=UTF8&s=electronics&qid=1266969199&sr=8-4
has anybody bought anything similar, and is it a fairly simple replacement, or is there any soldering involved - I'm wondering if the picture on Amazon's web page is accurate showing it with case backing on, or whether that's just an example, but you have to attach it to the existing cover on the stock battery (Amazon's web page doesn't say anything about it, and I know from experience with older Archos models - AV440 - that a replacement battery could involve dusting off the old solering iron).