This is the cheapest, most universal charger I've used, and it seems to work just fine. You could get a Triton2 or similar hobby charger for lots more functionality, but those are over $100, and you'd need a 12V PS to boot.
A lot of these hobby chargers are meant for RC use. RC batteries are often run extremely hard, with runtimes of 10 minutes or less. For this reason, RC hobbyists find it convenient to be able to charge their batteries in the field, powered by a 12V lead-acid battery.