Let's put it this way: If the next iPhone has a Dual-Core Cortex A15 architecture based CPU, LTE battery issues will be nothing to worry about.
For those that don't know what the difference is, I'll explain. The current iPhone 4S has a Dual-Core Cortex A9 based CPU which is manufactured using a 45nm process. Cortex A15 based CPU chips are manufactured using a 28-32nm process. These differences in size, although they may seem small, amount to HUGE differences in battery life. It is quite possibly, the difference between 2-4 hours more of battery life with the A15 based chip when compared to the A9 based chips.
Not to mention the fact that there are also manufacturing innovations for other parts that are also in the iPhone, for example, the
next iPhone is rumored to be using a much more energy-efficient Broadcom dual-band Wi-Fi chip that is manufactured using a new 40nm process down from the old 65nm process. And the new
LTE chips that is also rumored to be in the next iPhone will be significantly better at power management compared with LTE chips used last year/in early 2012.
And there's bound to be plenty more changes like this that will help to increase battery life. If you've been following Apple, you'd know that battery life is one of their highest priorities. Apple could have put LTE in the iPhone 4S last year, but instead chose to wait until LTE chips were more energy-efficient, because they'd rather stick with an older technology that consumes far less battery life rather than using a newer technology that sucks down battery life.
All of these things will add up to make the next iPhone VERY energy-efficient.