Does anyone have any experience with buying batteries from Ebay, Seidio and Mobi? It looks like they are respectively, super cheap, expensive, super expensive.

Ebay 1600 battery = $13
Ebay 2800 battery + case = $18
Seidio 1600 battery = $45
Seidio 3200 battery + case = $70
Mobi 2400 + case = $60
Mobi 3000 battery + case = $100

So any suggestions? I'm very tempted to buy the $13 1600 mah from eBay, but I'm worried that it would die in like 2 days or so...

Thoughts?

I'd personally avoid eBay unless it's a seller you can somehow verify as offering a working product. There are plenty of stories about batteries that don't actually offer increased capacity, many of them referring to "branded" sellers. eBay would only magnify those concerns. Unless you can be sure that the battery that's being offered is as promised and does increase capacity, I'd avoid it.

Typically, I'm very skeptical of large capacity increases that don't correspond to large form factor increases. LIon batteries achieve capacity in correlation to their size, so unless there's a great deal of dead space in the standard battery (certainly possible), I look at any significant growth in power storage that occurs in a battery of very similar or identical proportions. So I'd encourage you to stick with products where you can find good reviews from known manufacturers and sellers.

Yes, the folks selling at Ebay are pretty well established. So I'm not worried about the seller. I'm worried about the battery being "not as good" as the Seido or Mobi. I suppose for $13 for the 1600 mah battery, I only have $13 to lose! From 1350 mah (original) to 1600 mah is very feasible. So maybe I answered my own question, but I was hoping others would chime in on their own experiences.

I noticed that you have the FUZE. I'm also actually considering "upgrading" to that. Per chance, did you used to have a Tilt and upgraded? If so, is it worth it? Thanks in advance!

I had the unbranded TyTN II and not the Tilt, which was slightly different. But particularly with the ROM that HTC just released for the Fuze, I'm very pleased with the upgrade and think it well worthwhile. I thought it worthwhile before, but the ROM they released is faster, more stable, and fixes annoying GPS issues. Highly recommended.