It all depends on what battery you are using at the moment and what you are vaping at. If your vaping under 40 watts, and not using either the LG Browns or the Samsung pinks, I would suggest swapping for them, both are 3000mah batteries. IMHO, the samsungs are better than the LGs. Above 40 watts and your looking at Samsung 25Rs or LG reds both are 2100mah batteries.
Under 40 watts again, a 26650 like the pico mega or the vf stout could be the answer, I have a pro xvo DNA 40 and the batter lasts me 3 days on an efest green 4500 mah. 26650s are great, if you can handle the size but are not design for high wattage vaping as there's shed loads of voltage drop and your get weak battery around about 50% mark if you do.
Above 40 watts and its best to go for a dual battery setup, there's loads about.. The fan favourite is the hex ohms but you really need to know your ohms law. There's in sigieli 100w/150w which is good for the money, and there's the noisy cricket II which if it lives up to what it says it does on paper; will likely take over the hex ohms; but again noobies shouldn't really apply.