There are millions of cell phones in use throughout the world and only a handful of these stories about batteries exploding. Basically its a very rare occurrence thats not supposed to happen.
Avoid using generic or low quality chargers and replacement batteries. Make sure your phone can dissipate heat when charging, meaning don't place it under a pillow, etc. Do these two things and you'll never have to worry. Theres always the rare chance of a manufacturing defect, but for 99.9% of users they'll be fine.
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Motorola Droid Bionic
Stock 4.1.2 Rooted
CM11 4.4 Safestrap