Bạn nhớ sạc điện thoại tối nay nhé; sáng mai đừng để hết pin khi đang đi xe buýt.

Yes, it can be omitted.

Bạn means you, and it makes the reminder explicit. In everyday Vietnamese, if the listener is already obvious, people often drop the subject:

Nhớ sạc điện thoại tối nay nhé.

That sounds very natural too. Keeping bạn makes the sentence a little clearer and slightly more neutral, which is common in learning materials.

In this pattern, nhớ means remember to do something.

So nhớ sạc điện thoại means remember to charge the phone.

This is a very common structure:

• Nhớ gọi mình nhé = remember to call me
• Nhớ mang ô = remember to bring an umbrella

It does not mean to miss here. Vietnamese nhớ can mean both remember and miss, so context matters.

Vietnamese often leaves out possessive words like your when the meaning is obvious from context.

So sạc điện thoại here naturally means charge your phone, even though your is not said.

If you wanted to make it fully explicit, you could say: sạc điện thoại của bạn

But in normal speech, that often sounds unnecessary.

Yes. Sạc is the everyday verb for to charge electronic devices.

A few related expressions are:

• sạc điện thoại = charge the phone
• cắm sạc điện thoại = plug the phone in to charge
• sạc pin = charge the battery

So sạc is perfectly natural here.

That word order is very natural in Vietnamese. Tối nay means tonight, and here it tells you when to do the charging.

Vietnamese time expressions are flexible. You could also say:

Tối nay bạn nhớ sạc điện thoại nhé.

That version puts more emphasis on tonight. Both are correct.

Nhé is a sentence-final particle that makes the reminder sound softer, friendlier, and less abrupt.

Without nhé, the sentence is still grammatical: Bạn nhớ sạc điện thoại tối nay.

But that sounds more plain and a little firmer. With nhé, it feels more like:

• just a friendly reminder
• okay?
• please remember, alright?

It is one of those words that often does not have a single perfect English translation, but it strongly affects tone.

The semicolon links two closely related ideas:

1. charge the phone tonight
2. do not let it run out of battery tomorrow morning

It shows a stronger break than a comma, but the two parts still belong together.

In normal writing, a period would also work: Bạn nhớ sạc điện thoại tối nay nhé. Sáng mai đừng để hết pin khi đang đi xe buýt.

Vietnamese often puts time expressions near the beginning of a clause to set the time frame right away.

So sáng mai tells you immediately that the warning applies tomorrow morning.

This is very natural: Sáng mai đừng để hết pin...

You could move time expressions around in some cases, but the sentence usually sounds clearer this way.

Đừng is the usual way to make a negative command or warning. It means don’t.

So:

• đừng đi = don’t go
• đừng quên = don’t forget
• đừng để hết pin = don’t let it run out of battery

It is a very common word in spoken and written Vietnamese.

Here để means to let or to allow.

So đừng để hết pin literally means: don’t let it become out of battery

More natural English would be: don’t let it run out of battery or don’t let the battery die

This use of để is common:

• Đừng để cửa mở = don’t leave the door open
• Đừng để đồ ăn nguội = don’t let the food get cold

Hết means finished, used up, gone, and pin means battery.

So hết pin means:

• out of battery
• battery dead
• battery drained

It describes a result state.

Related expressions:

• pin yếu = low battery
• sắp hết pin = about to run out of battery
• hết pin rồi = it’s out of battery already

Because it is already understood from the first clause.

After sạc điện thoại, Vietnamese can naturally leave the phone unspoken in the next clause: đừng để hết pin

The listener understands that the phone is what might run out of battery.

If you want to make it fully explicit, you can say: đừng để điện thoại hết pin

That is also correct, just a little more spelled out.

It means when / while you are riding the bus.

Breaking it down:

• khi = when / while
• đang = marks an action in progress
• đi xe buýt = go by bus / ride the bus

So khi đang đi xe buýt emphasizes that this is happening during the bus ride, not before or after it.

Đang shows that an action is in progress.

Without đang, khi đi xe buýt can still mean when riding the bus, and it is also natural. But khi đang đi xe buýt more clearly highlights the ongoing situation:

while you are in the middle of riding the bus

So đang adds a stronger sense of right then, in progress.

Vietnamese commonly uses đi + means of transport to mean travel by that vehicle.

Examples:

• đi xe buýt = go by bus / ride the bus
• đi xe máy = go by motorbike
• đi tàu = go by train

So đi xe buýt is the normal way to say ride the bus. Even though the literal word đi often means go, in this pattern it refers to traveling by that mode of transport, not specifically walking or physically going somewhere on foot.