Clearly, this question is only in regard to smoke alarms that require non-sealed batteries. Any other model will never see the need for this question, so be aware of that. Okay, in terms of what types of batteries you should use in a smoke alarm, start off by figuring out what type your new model takes. Some will take AA, some AAA, and others will even take nine-volt batteries.
Either way, you really should not go the cheap route and should invest in a well-known branded pair of batteries. For instance, lithium smoke detector batteries are great for smoke alarms. Oh and also, never use rechargeable batteries as there charge is simply too inconsistent.