[JASJAR, XDA Exec, MDA Pro Accessories] sl9:
I've just purchased my THIRD extended battery for my MDA PRO, and I have learned quite a lot over the past few years so I will share some of this information with you, in the form of a buyer's guide to getting a new battery for your HTC Universal.

Types

There are THREE different physical types of replacement battery (PU16A) available for the HTC Universal. These are:

Standard (original) type battery. These are the same size as the battery that came with your Universal when you originally purchased it, so they do not increase the size or weight of your device and do not need a new back cover. They vary in rated capacity from 1600 to 1750mAh, and are the cheapest to buy.

Extended battery. There are 3 or 4 different brands of this type floating around, and they vary in rated capacity from 3150 to 3800mAh. At the moment the 3150mAh 'Cameron Sino' brand is by far the most widely available on eBay. These are also cheap, and actually offer the best price/mAh rating of all (bang for buck). These also significantly increase the size and weight of your device, and they require a new back cover (which should always be included when you buy the battery).

Ultra extended battery. There are 3 different brands of this type: The 4800mAh 'Cameron Sino' which is the cheapest, the 5000mAh Worcell which is a LOT more expensive, and at the very top we have the 5200mAh Mugen which is VERY expensive indeed. This type of battery increases the size and weight of your device even further, and includes a new back cover which is larger than the one found on 3xxx mAh batteries (although in my opinion it does look better!).

My main point is that within each type, the various different brands of battery are all

physically identical

, that means they have exactly the same components as each other. It is possible that they may have been made in different factories, eg. some in Japan and some in China, although to be honest I doubt this as it just does not make financial sense to produce this product in anywhere other than 1 factory.

Quality issues

The first 3200mAh battery I purchased was faulty, my phone just displayed a red light and refused to boot no matter what I did. The replacement was fine however, and I have been using it until today as my new 4800mAh battery has just arrived :D

Reading through these forums, it seems that quite a few people have experienced the "red light" issue on new batteries purchased from eBay sellers in Hong Kong. This is not common at all, but there is a small risk that it can happen.

In my opinion though, the massive amount of money you can save by purchasing the battery from eBay is more than worth this risk (all sellers should replace faulty batteries anyway). The 5200mAh Mugen battery for example is nearly five times more expensive than a Cameron Sino 4800mAh from eBay, and this is close to the actual cost of an entire second hand HTC Universal! So from the Ultra category I think only the 4800mAh battery is good value, the 5000 and 5200 models are just FAR too expensive for such little extra benefit - which you are highly unlikely to notice anyway.

Coming soon: Photographs of the 3 different types of battery that are available.