I have purchased quite a few backup batteries for both Canon and Sony and never had issues, but I think it helps to look for brands that have had enough sales (on Amazon or a similar site with user reviews) to avoid the "bad ones". Definitely do not go for the cheapest you can find if there are any hints that it could be a compromise in quality. If the battery leaks or blows up or somehow damages the camera, your cheap battery will end up being quite pricey, so err on the side of caution. The other thing that works well is to charge your camera, inside your bag, when you wouldn't otherwise be able to plug in. You can use an inexpensive external USB battery without voiding your camera warranty and for a fraction of the price. And high-capacity USB batteries can recharge a camera battery several times.