To infringe on a patient, you must infringe on all claims. If they have patented a battery sleeve with an integrated boost converter, than the only way to infringe on that patient is to make a battery sleeve with integrated boost converter. Any other boost converter is not a infringement.
This is why companies like Microsoft and Apple tend to get many many very specific patients, rather than a single big patient covering an entire device. For example, when Apple sued Samsung over patient infringement, they didn't claim they violated patients on a iPhone. They had patients such as Design Patent 504,889, for which the claims consist of a single sentence, describing a rectangular electronic device with rounded corners. Because the patient made no other claims, any rectangular device with rounded corners infringed on that patient.