Replacement battery is new, straight from Dell.

Have been through various things with Dell - BIOS upgrade, etc

Basically the 16 cell battery (replacement, new), which I was told should last 6-7 hrs, lasted approx an hour. Battery charges back up to 100% when connected to main.

I've also just noticed that it's got no subwoofer - wasn't told about that before I bought it.

Does anyone know the best way of dealing with Dell?

I called them a while ago and was on phone for ages as mentioned and they didn't solve it. I was on an online chat session for almost an hour today and that didn't solve it.
I tried calling again but didn't get through to anyone and was on hold for ages on a national rate line.
I have sent an email but from previous experience it was passed around and no one dealt with anything.

What is the best of having something ACTUALLY DEALT WITH and letting them know of these experiences?
I have a 3yr next day on-site warranty but no one comes out, I just get told to try things on the phone at my expense.

Is the replacement battery new, or used? Used or not, lithium ion batteries run about 18 months before they no longer hold a sufficient charge - if the battery was used, it may be near the end of its useful lifetime as well.

You mean the motherboard?