Mobile phone accessories maker PowerSkin recently expanded its line of battery-boosting smartphone covers by adding power sleeves for two HTC handsets.

In addition to the iPhone, the Samsung Galaxy S 4G and Vibrant and a number of others, PowerSkin is now offering battery cases that support the Android-based Inspire 4G and Desire HD.

With the battery-extending silicone rubber case, PowerSkin promises an additional eight hours of battery life. The cases are designed specifically for the two HTC handsets and include holes for the cameras and outlets.

"With twice the power for your smartphone, your life charges on. You can keep working. Keep playing. Keep moving. PowerSkin is your go-to, go-anywhere, go on-and-on power source. Because battery life is life," the company said on its website.

Additionally, the sleeves come with a one-year limited warranty, PowerSkin stated.

HTC's position in the smartphone market has expanded drastically within the last year. According to recent figures from IDC, HTC increased its market share from 4.9 percent to 8.9 year over year in the first quarter of 2011.