Thank you for taking him in...does he have a bright white basking bulb as well? You mentioned a "heating pad", but that isn't really necessary and won't keep his temperature zones in the proper ranges, especially his Basking Spot Surface Temp, which needs to be between 105-110, Hot Side Ambient (air) Temp between 88-93, and the Cool Side Ambient (air) Temp between 75-80. Beardies get all of their heat from above or they should), and both a proper UVB tube (mounted within the correct distance from his Basking Spot/Platform and unobstructed by any mesh lids) and a bright white basking bulb need to be directly over his main Basking Spot/Platform in the Hot Side of the tank. He needs to be able to get both lights at the same time while basking on his main Basking Spot, as this is how you replicate natural sunlight.
Typically when a baby is listless and has little to no appetite and doesn't want to hunt, it's due to an improper, inadequate
UVB light and improper temperature zones, as well as too short a photoperiod for both of these lights to be on, which should be 13-14 hours every day.
Also, if you're using a Coil
UVB bulb this can cause severe eye damage and vision issues, as well as neurological issues that can stop them from hunting and eating. You should never use any type of Coil
UVB light for a beardie, and 99% of the Compact UVB bulbs (regular lightbulb shaped) sold are not even close to adequate for a beardie, they need long UVB tubes that are mounted within the correct distance of their basking spots and unobstructed by a mesh lid. So typically this problem is due to improper lighting and improper temperature zones, and can also be due to using only stick-on thermometers, like the round ones that are sold for reptiles or any type of "aquarium" stick-on thermometers. Stick-on thermometers make it impossible for you to measure his Basking Spot Surface Temperature (they only measure the "Ambient" or the air temps, which is the most important temperature zone for a beardie. Also, most all stick-on thermometers are terribly inaccurate and when tested are usually off by between 10-20 degrees. So if you're not using either a Temperature Gun or a Digital Probe Thermometer so that you can accurate temps, and most importantly so you can measure his Basking Spot temp, please invest $10 at Petco in a Digital Probe Thermometer.
Please post some photos of the baby, and then of his entire enclosure and his lighting, and then let us know the Brand, Model, Wattage, and Types (tube, compact, coil, Mercury Vapor) of both his
UVB light and his Basking Light, as well as the color of his Basking Light (bright white is the only color of bulb you should use for a beardie, no red, blue, yellow, green, purple, black, "moonlight", etc.). Also, what is his daily diet (normally if he was eating, or at least what you've been offering him), along with how often you are dusting his live insects with Calcium and with a multivitamin, and which multivitamin you use. Also, if you could list the Basking Spot Surface Temperature, the Hot Side Ambient (air) Temperature, and the Cool Side Ambient (air) Temperature for us, as well as telling us what type of thermometer you are using to take the temps, this info can help us figure out what's going on.
Hopefully this is just the typical husbandry issues that are causing his lethargy and lack of appetite, and some simple tweaking of his setup and some light upgrades/temperature adjustments will turn him around quickly, usually they perk up pretty immediately once they are put under adequate
UVB light and given a proper Basking Spot Temp...
I forgot to ask, do you know about how old he is? A better question might be how long did your friend have him, as if she bought him from a pet shop like Petco or PetSmart they are usually right around a month old when they are sold. Another good question would be about your friend's husbandry, meaning did she use the exact same setup that you have been using since you got him, or have you since upgraded anything? I'm asking this because, for example, let's say your friend had him for about a month, which would make him around 2 months old, and your friend was using a very weak compact or a coil
UVB bulb that was sitting on top of a mesh lid, and she only let his weak
UVB bulb and his basking bulb on for 10 hours a day, and then when you got him a few days ago you upgraded his
UVB light to a 22" Reptisun 10.0 T5HO UVB Tube that is mounted under the mesh lid and within 11" of his Basking Spot/Platform, and you have had both his T5 UVB tube and his bright white basking bulb on every day for at least 13-14 hours, that would mean that you've been providing him perfect UVB lighting for the few days that you've had him, but during the entire month that your friend had him he pretty much got zero
UVB light, and it will take a while for him to recover from not getting any
UVB light for an entire month...That's just an example that I made up, but you see what I'm getting at....