I will bring an extra charger ___________ my battery dies.

Correct answer: in case.
Complete sentence: I will bring an extra charger in case my battery dies.

• in case:
- Bangla Meaning: এমন ঘটলে; এমতাবস্থায়; যদি এমন ঘটে।
- কোন ঘটনার সম্ভাবনা বুঝাতে in case ব্যবহার হয়।
- অর্থাৎ, পূর্ব সতর্কতা হিসেবে 'যদি অর্থে' যে কাজটি ঘটতে পারে তার পূর্বে "in case" বসে।

Other options:

ক) although
- Used for contrast, not precaution.
- যেমন: Although she is young, she is independent.

গ) yet
- Used to show contrast or something unexpected.
- যেমন: She was tired, yet she continued to work late into the night.

ঘ) otherwise
- Means "or else" and introduces a negative consequence.
- যেমন: Study hard, otherwise you will fail in the exam.

Source:
1. Merriam-Webster dictionary.
2. Accessible Dictionary.
3. Cambridge Dictionary.