Hi, and welcome Kay93, I have a steampunk and your issue isn't so much the batteries, but the fact that you are running that setup at its MAX setting. Because it is a regulated mod, as your batteries start to drain and lose power, your mod is going to give you that reading once it feels that it cannot draw more power safely from your device (I realize I'm personalizing your steampunk, rather, the safety mechanisms that are in place with your device are going to stop you from pulling power. What device is your husband using, and does he use less watts? Also, each board on each mod will handle this slightly differently, the Steampunk seems to do a very efficient conversion of power, meaning that when I got mine, I was turning DOWN all my wattages, since it was a more "powerful" device, I ended up using lower wattages.
If the aspire setup is sill able to run those batteries for a longer time period at the same wattage, which I'm not sure you specified, is it a 200w mod, perhaps converting the power more efficiently, or, if the wattage that your husband is using is much lower, it will be safer for that mod to convert battery power from the charge left in the batteries, because it is not putting an unsafe "strain" on the batteries, or the power chip is converting power less efficiently.
Generally, it's not the greatest idea of all time to run any mod at its "top" wattage as it does place a strain on the device and batteries, though switching to more powerful batteries may give you more run time, though I can run my LG HG2 batteries all the way down to "low battery" if I want, though I usually switch them out when the power bar goes down to about 1/4 to save strain on my batteries as well, though certainly not every time if I'm not paying attention. Keep in mind I am running nowhere near the wattages you are on the Steampunk, which is why I'm not running into issues.
Think of wattage as like the speedometer on your car. Just because mine goes up to 200 miles per hour, that certainly doesn't mean I'm going to run it at that speed, all the time, or even ONE time (though, I have accidentally fired my Steampunk on 120 watts, and I was able to fry a coil into oblivion fairly easily with one puff) so it's DOABLE, it just may not be advisable to do all the time. I'd suggest seeing if you can go lower on watts with your vape, even if you are running a sub0hm setup on top of it. 120 watts on a steampunk is pretty powerful. You'll be ABLE to do it, I wouldn't *recommend* doing it, it overstresses the mod and the batteries to take a mod up to its very highest tolerance. If you want to run that wattage, I'm not sure the steampunk is your device, you may want a 3 or eve 4 battery setup stating it's capable of like, 250 watts or more, even though I'd never run THAT device as high as 250 watts, either. But if you want to routinely vape 120 watts, I'm not sure the Steampunk is your mod to do that with. You might look into an RTA and temp control coils, unless your tank offers TC capable coils, you then set the temp to a "safe" temp, and vape without so much dependence on wattage, and the Steampunk is pretty good at TC. You can set a "ramp up" wattage, but the TC handles the rest, and I'm guessing that if you were to choose a safe temp, the wattage you'd be running would be lower, though you may find you enjoy that vape. You may also find turning down your wattage by a fair bit (say, at least 20--30 watts, if not more) may help with battery life and your overall safety in general. The highest wattage a mod can go is not usually the best demonstrator of its true capabilities, and the steampunk is so efficient with power, I am guessing you are actually going quite higher than you *think* due to its board.
I hope this helps. You could certainly try other batteries, and that may help you some, but I do remain concerned at running a mod at MAX capability. It may cause the batteries to get warm, overstressing them as well. If you must have 120 watts (or higher!) I'd suggest a different mod.
That's just me, I am naturally cautious. But you may be surprised at the results of simply bumping your watts down a fair bit and seeing how the vape is, possibly with different airflow, or different VG/PG mix if you want huge clouds.
I hope this helps. Good luck!
Anna