Refurbished Latitude 5400 has awful battery life

Report the issue to EBay and request a refund or a new battery.

Worn battery capacity is never as good as the 76% indicated in your case and about an hour is typical of the degradation experienced as soon as 2 years old, depending on cycle count and charge/discharge depth. In my time of owning and repairing Laptops I've never seen the calculated capacity be even close to accurate and anything lower than mid-90s is basically completely worn. Capacity in Lithium pouch cells used in Laptops (i.e. post 18650 cylindrical packs, often external) is anything but linear and predictable and they never come close to advertised life.

Anyway, your options are 1. dispute/return with Ebay if within whatever their window is or 2. replace the battery yourself if you're otherwise happy with the laptop. Genuine batteries are way overpriced new and never make sense on older Laptops; there's a lot of $30 aftermarket batteries on Amazon that work well with tons of reviews and I've never had a problem using them in repairs. Genuine batteries from a reseller are often old production and worse then aftermarket batteries, while also being more expensive.

You can enter your service tag on Support to see the parts list somewhere on there, and you just search for the 5-digit battery code to find a replacement. Every Dell laptop has a detailed service guide on support documentation and you only need a #1 phillips screwdriver to remove the base cover to replace it.

@ejn63​ I have purchased two "refurbished" lap tops over the years and both came with useless or nearly useless batteries that needed replacing. 

1) Go go the sellers site or pull up the description of the one you purchased and you should find some small print disclaimers about what  their definition of "refurbished" is. I haven't read one yet that doesn't include a legal disclaimer about the battery life not being excluded from the warranty. Different companies have different policies but the sad reality is from my experience is that "refurbished" laptops have basically benen turned on to make sure the screen and keyboard were functional, passed a hardware diagnostic, had the HD wiped (if not wiped already when they acquired it), reset the BIOS to the original boot settings and had a fresh OS installation.

My first refurshied was an HP over ten years ago that was my first laptop and came  with a completely useless battery. It literally had ten minutes of battery life if I was using the internet and maybe 15-20 mintues just using Word or Excell.

When I contacted the company I purchased it from they informed that batteries were considered normal wear/replacement items that were not part of their assessment, refurbishing or covered under the 90 day warranty.

It had also been advertised as having a CD-R drive in the item description and I had purchased it as a back up to my desktop and to take with me on trips or vacations where I expected to do some photography with my DSLR and wanted to review and back up pics before I got home. Months after purchasing it and three months after the warranty expired I spent a good 20-30 minutes on a cruise trying to burn pics to a CD-R only ro discover the drive was CD/DVD play only!

Contacted the company when I returned and they acknowledged that it had been listed as having a CD-R installed but since it was past the 90 day warranty they refused to even send me a used replacement CD-R to swap out with the play only drive that came with it.