أوه، بطارية الهاتف ضعيفة.

In Modern Standard Arabic, the present tense usually does not use a separate verb for is / am / are.

So:

• بطارية الهاتف ضعيفة
• literally: The phone battery weak

But it means:

• The phone battery is weak.

This kind of sentence is called a nominal sentence.
If you want was, will be, and so on, Arabic does use extra words or verbs, but in the simple present it normally leaves is unstated.

This is an iḍāfa construction, often called a genitive construction or noun + noun possessive structure.

• بطارية = battery
• الهاتف = the phone

Together:

• بطارية الهاتف = the battery of the phone = the phone battery

A few key points about iḍāfa:

• The first noun usually does not take الـ.
• The second noun shows the definiteness.
• If the second noun is definite, the whole phrase becomes definite.

So even though بطارية has no الـ, بطارية الهاتف still means the phone battery, not just a phone battery.

Because that is how the iḍāfa structure works.

In بطارية الهاتف:

• بطارية is the first part of the possessive phrase
• الهاتف is the second part

The first noun in iḍāfa normally appears without الـ, even when the whole phrase is definite.

Compare:

• بطارية هاتف = a phone battery / battery of a phone
• بطارية الهاتف = the phone battery

So the definiteness comes from الهاتف, and it makes the whole phrase definite.

Because it describes بطارية, and بطارية is a feminine noun.

Arabic adjectives must agree with the noun they describe in things like:

• gender
• number
• definiteness

Since بطارية is feminine singular, the adjective must also be feminine singular:

• masculine: ضعيف
• feminine: ضعيفة

So:

• بطارية ... ضعيفة
• not بطارية ... ضعيف

Because ضعيفة here is not an attributive adjective inside the noun phrase; it is the predicate of the sentence.

Compare these two ideas:

1. The weak phone battery
   This is one noun phrase. In Arabic, an adjective directly modifying a definite noun would also be definite.

2. The phone battery is weak
   This is a full sentence. Here weak is the predicate, so it is normally indefinite.

That is why Arabic says:

• بطارية الهاتف ضعيفة
• not بطارية الهاتف الضعيفة for the meaning The phone battery is weak

If you said بطارية الهاتف الضعيفة, that would mean something more like the weak phone battery.

Yes, and this is a very useful point.

The final ة is called tāʾ marbūṭa. Its pronunciation changes depending on context.

When a word stops by itself, it is usually pronounced like -a:

• بطارية ≈ biṭṭāriyya

But in an iḍāfa, because another noun follows it, the ة is pronounced as t:

• بطارية الهاتف ≈ biṭṭāriyat al-hātif

So learners often miss this, but in this sentence you should hear a t sound connecting the two words.

In fully vocalized formal Arabic, it would be:

• أوه، بَطَّارِيَّةُ الْهَاتِفِ ضَعِيفَةٌ.

With grammar labels:

• بَطَّارِيَّةُ = nominative, because it is the subject/topic of the nominal sentence
• الْهَاتِفِ = genitive, because it is the second term of the iḍāfa
• ضَعِيفَةٌ = nominative predicate

In normal writing and everyday reading, these short vowel endings are usually omitted, so learners typically see:

• أوه، بطارية الهاتف ضعيفة.

أوه is an interjection, like Oh! in English. People will understand it, and it can appear in writing, dialogue, and informal contexts.

However, in very formal MSA prose, writers may simply leave it out. So:

• أوه، بطارية الهاتف ضعيفة. = natural in dialogue or expressive writing
• بطارية الهاتف ضعيفة. = more neutral and plain

So yes, it works, but it adds an emotional reaction rather than essential grammar.

Yes, but بطارية الهاتف ضعيفة is the most straightforward and neutral order.

This is:

• subject/topic: بطارية الهاتف
• predicate: ضعيفة

Arabic can be flexible, especially for emphasis, but for learners this order is best.

So if your goal is simply The phone battery is weak, stick with:

• بطارية الهاتف ضعيفة

Literally, ضعيفة means weak. With batteries, that often corresponds to English ideas like:

• weak
• low
• running low

So بطارية الهاتف ضعيفة can naturally convey that the battery is low or not strong.

If you specifically wanted to say the battery is completely dead, Arabic might use other expressions depending on context. But for a general warning that the battery is low/weak, ضعيفة works well.

Yes. In MSA, a simple present-tense nominal sentence is often negated with ليست for a feminine singular subject.

So:

• بطارية الهاتف ليست ضعيفة
• The phone battery is not weak

Why ليست?

Because بطارية is feminine singular, and ليس agrees with the subject in gender and number.

Compare:

• masculine singular: الهاتف ليس جديدًا
• feminine singular: البطارية ليست ضعيفة

This is a very useful pattern to learn early.