Battery life on most SRM units in the current line-up is 1,700 hours of use. That is more than 3 years for most riders. Some units have lower capacity due to the available space in the spider (e.g., 2x10 MTB units).

While I generally prefer user replaceable items where all else is equal, if one has no soldering skills, sending the crank in to SRM once every 3-5 years where they will check it over thoroughly while they have it is probably not a bad thing.