FugouSell 4700mAh Battery Case for Galaxy S9
The FugouSell battery case promises to add 120% more battery life to your Galaxy S9 and is designed to prevent your phone from overheating; you can turn off the battery on this case as needed as well. It's also a protective TPU case, so you can expect safeguarding from everyday drops, bumps, scratches and scrapes.
One feature we like is that its magnetic at the back, which means you can easily attach it to a magnetic car mount (see our round up of the best car mounts here) without having to switch your phone case.
You get a lifetime warranty with FugouSell and a 30-day money back guarantee too.
Moonmini 4700mAh Battery Case for Galaxy S9
We previously featured the Moonmini in our round up of the best iPhone X battery cases, and we're happy to see there's one for the Galaxy S9 as well. There's a 5200mAh version for the S9 Plus (£24.99 in the UK, or $27.99 if you're in the US).
The Moonmini battery case will not only keep your Galaxy S9 charged with its 4700mAh capacity, but will also protect your S9 from scratches and dirt. With easy access to all buttons and ports, you can charge your phone and case at the same time.
An LED indicator at the back of the case also lets you know how much juice is left. If you have any issues, Moonmini offers a one year warranty.
i-Blades SmartCase 1800mAh Battery with Memory
The SmartCase from i-Blades is slightly different from other S9 battery cases out there because the battery is not housed within the case itself. It also expands your S9's memory capacity (hence "SmartCase").
The SmartCase offers a modular design that let you add and replace functions to the case as separate attachments. The battery, in this case (pun maybe intended), takes advantage of the S9's wireless charging capacity and snaps on to the back.
This snap-on-snap-off design helps reduce bulk so you'd only add the battery (or "Smartblade" as they call it) when you need it. The Smartblade/battery also expands the 16GB storage capacity to 64GB. You can increase up to 288GB with the built-in micro SD slot.
Our only qualm with the SmartCase is that the battery only packs 1800mAh. But in return, you do get a well designed case that cleverly manages bulk issue (and did we mention you also get an "EnviroSensor" that provides real-time feedback on the air quality?).
ZeroLemon 5200mAh Battery Case for Galaxy S9 Plus
The ZeroLemon case for the S9 Plus packs 5200mAh of power, and like the Moonmini has an indicator to tell you how much charge you have left. You can also turn the battery on and off as desired.
It's a TPU case, so expect a rubberized, non-slip feel. It should also keep your S9 Plus safe from scratches, drops and scrapes. It offers easy access to the charging port, so you can connect your S9 Plus to your computer without having to take the case off.
The S9 version is available in the US only, and can be found on Amazon for $29.99.