Some people consider electronic tuners a crutch, but in loud environments, or for tuning discreetly, they are practical necessity. When I started playing guitar, electronic tuners where kind of expensive, and unless you sprung for the Boss TU-12, they weren't particularly road worthy. But today, the tuner market is pretty much dominated by pedal board based solutions, and the ubiquitous and inexpensive clip-on tuner. Since I spend most of my time playing acoustic instruments without a pickup or transducer, the clip-on is the solution of choice for me. 

The first generation of low cost clip-on tuners weren't particularly accurate or durable. They always seemed to stop registering signal well after a while. When the Snark line was introduced, they really seemed to improve both the accuracy and durability problems, and at a bargain basement price.  But even improved, they always seemed to eventually stop performing well, but continue to soldier a while before the battery actually died. I assumed the problem was just wear and tear, so that the device no longer made good contact, and stopped being able to detect the vibrations. Wrong.

I finally realized that it was the battery running low that caused the performance drop off. Once the battery got below that point and the performance started to suffer, there was still plenty left to power the tuner for a significant while, just with terrible performance. Once a tuner got a low battery, I would have to remember to swing by a drugstore to pickup a replacement. Buying one or two watch batteries at time at retail is expensive ($3-$5 per battery for a $10-$20 tuner), and I always seemed to find the one drug store that had just run out of that most common of watch batteries, the CR2032. Or I'd forget the number and buy a CR2025 by mistake. 

Then I figured out the lifehack that made living with Snarks so much better: buy the batteries in bulk on Amazon! For the cost of two batteries at a drug store, you can get blister packs of TWENTY ($7.96 for 20, instead of $7 for two at Walgreens).

At that price, I basically take one sleeve of batteries and one snark tuner, and keep a set of both in each guitar case. As soon as one of the Snarks starts to act crappy, I just replace the battery, and they go back to working great. 

Snarks are easy to leave "On" all the time while playing, so just be mindful of turning it off once you're done will go a long way to improving battery life. 

So, I usually go for the SN-8 "Super Tight" Snark, which apparently has better accuracy. I sprung for the more expensive HZ1 Snark tuner, but I didn't find it's performance worth the additional cost, and it's bright white color draws too much attention on stage.

I have also had success with the D'Addario NS Micro Clip-On Tuner. It's super low profile design worked great on the headstock of my 1939 L-5, but didn't really fit well on some of my other guitars. But bear in mind, those use a different battery, the CR2025, but you can get those in blister packs on Amazon as well.