Samsung Galaxy S8 is suggested.
Operating System is Android Nougat 7.0
Priced from RM3299
Battery: 3,000mAH, Non-removable
The screen is 5.8” Quad HD, Super AMOLED, 571 PPI (68.1 x 148.9).
Size not too big is easy to hold in palm....

Flagships: Huawei Mate 10/Mate 10 Pro, OnePlus 5T, Google Pixel 2/2 XL or Sony Xperia XZ1 Compact(don't underestimate Sony's battery optimisation, if only Sony put an even bigger battery)
Mid range: Xiaomi Mi Max 2, Xiaomi Redmi Note 4X, Lenovo P2, Oukitel K10000 Max
Entry level: Redmi 4A, Redmi 4X, Oukitel K10000

All the above have best battery life in their respective category.

Oh sorry, some mistakes. OnePlus 5T and Sony XZ1 Compact is not dual SIM, Google Pixel 2/2 XL is technically speaking dual SIM not dual SIM. The others listed in each other category are dual SIM. Here is an updated list.

Flagships: Huawei Mate 10(Hybrid Dual SIM, one nano SIM slot, one micro SIM interchangeable with SD card slot), Huawei Mate 10(Dual nano SIM), Google Pixel 2/2 XL(Dual SIM, one nano SIM slot, one eSIM slot)

Mid range: Xiaomi Mi Max 2(Hybrid Dual SIM, one nano SIM slot, one micro SIM interchangeable with SD card slot), Xiaomi Redmi Note 4X(Hybrid Dual SIM, one nano SIM slot, one micro SIM interchangeable with SD card slot), Lenovo P2(Hybrid Dual Nano SIM, one nano SIM interchangeable with SD card slot), Oukitel K10000 Max(Hybrid Dual Nano SIM, one nano SIM interchangeable with SD card slot)

Entry level: Redmi 4A(Hybrid Dual SIM, one nano SIM slot, one micro SIM interchangeable with SD card slot), Redmi 4X(Hybrid Dual SIM, one nano SIM slot, one micro SIM interchangeable with SD card slot), Oukitel K10000(Dual micro SIM)

You're welcome, happy to help out. Your main focus is on dual SIM slots and battery life, and those phones fit your criteria. In my opinion, the ones I recommend in each category based on overall day-to-day use is as follows.

Flagship: Huawei Mate 10 Pro
Mid range: Xiaomi Mi Max 2, if you prefer smaller screen than Mi Max 2 choose Redmi Note 4X.
Entry level: Redmi 4X

Since you are leaning towards the phone, I'm going to list the cons and pros of the phone.

Here are the cons of the Huawei Mate 10 Pro.
1. There is no SD card slot. You cannot expand storage for the phone with SD card. The way to overcome this problem is to backup photos, videos and documents to an online cloud(for example Google Photos, Google Docs etc.) then delete the photos, videos, documents on your phone to allow more storage on your phone.
2. There is no 3.5mm headphone jack. The way to overcome this problem is wireless earphones, audio quality may not be amazing but it is decent.
3. The back is glass. It's glass and it's fragile. The way to overcome this problem is to buy a case, skin etc.
4. There is no wireless charging. Although the back is glass, the phone doesn't have wireless charging. The way to overcome this problem is to use the USB C port to charge.
5. The screen is only FHD+ resolution. The quality of VR using this phone may not be as good as 2K or WQHD displays.
6. It has no portrait mode. Personally, I don't consider this as a con, but for some it is a deal breaker.
7. It uses EMUI. The UI is too iOS like, I personally don't like that but some people see that as a pro.

Here are the pros of the Huawei Mate 10 Pro.
1. It is dual nano SIM. You can fit two nano SIMs in the phone.
2. It is IP67 water resistant. You can splash your phone with water and wash the dirt off your phone, just don't drown your phone with brute force.
3. It has great battery life. You can use it all day from today's morning and be left with some charge until next morning.
4. It uses the Kirin 970 NPU. Normally, a smartphone with a CPU will degrade its battery faster but Huawei Mate 10 Pro is one of the first smartphone OEMs to use a NPU on a smartphone, so it won't the degrade the battery as fast as other flagships.
5. It has a dual f/1.6 standard+monochrome dual camera setup for stunning low light shots. It takes amazing photos, some are even better than DSLR.
6. It has Project Treble support. Huawei "can" support this phone for up to 6 years. Before a smartphone OEM can only support it for about 2 years. But will Huawei continue supporting it for 6 years, that's the question.

"Portrait mode" is a camera shooting mode in which you blur out the background to give Bokeh effect. OnePlus 5T, Google Pixel 2/2 XL, iPhone 7 Plus have that mode and calls it "Portrait Mode", Samsung calls it "Live Focus".