If your phone allows access to the battery, another (spare) battery might be a good remedy. If not, any of the new line of power bricks will suffice.

Other people carry around solar powered cellphone chargers to avoid the same inconveniently low-battery situations you've just recently experienced.

Of course, this would all be moot if we had better battery technology and/or ubiquitous, wireless charging.

And I believe we'll both see it in the near future.

Namaste, JaiChai