If you rely on mobile devices all day, every day, then having a power pack with you to top them up when they get low on juice is a must. And despite what you might think, they don’t have to be big, bulky units that weigh down your bag.

Take the LithiumCard, for instance: It’s small enough to fit in your wallet and it boasts HyperCharging technology for rapid power when you need it — and thanks to Cult of Android Deals, it’s just $39.99 (down from $55) for a limited time. But you’ll have to act fast to take advantage of this awesome offer, because it’s ending soon!

The LithiumCard is as thick as just 5 credit cards, so it will comfortably slip into most wallets and you won’t even know you’re carrying it until you need it, and a NanoStik pad is also included so that you can stick the LithiumCard to your device itself while it’s in use without leaving any sticky residue when it’s removed.

The LithiumCard has an aluminum housing so it looks great, and it’s available with a Lightning connector for Apple devices or a microUSB for just about every Android-powered smartphone or tablet on the market. It’s packing a 1,200mAh battery that charged via the built-in USB connector, and it outputs up to 2 amps of power.

Its size isn’t the only thing that makes the LithiumCard special. It also boasts HyperCharging technology, which provides your devices with rapid power when they need it most. With up to 1% of battery life every minute, it takes just 20 minutes to take your device from zero to 20% battery life.

You can order your LithiumCard from the Cult of Android Deals page by clicking the button below. This offer ends tomorrow, at which point the price will go back up to $55, so get yours with 27% off while you can by clicking the button below.