Complex sentence: A molten-electrolyte battery is activated by igniting a pyrotechnic heat source; the battery delivers current for a short time (seconds to a few minutes), but some thermal batteries can be stored 10 years or more without deterioration.
Split into simpler sentences: A molten-electrolyte battery is activated by igniting a pyrotechnic heat source. The battery delivers current for a short time (seconds to a few minutes), but some thermal batteries can be stored 10 years or more without deterioration.