One of my hobbies is hosting a bunch of old 3g devices in my closet that I've modded to run w/o battery..something like 150+ that I use for mining/passive income. I want to keep adding more

The closet's got a small server and a window A/C unit. Some of the devices intermittently lose data/3g connection which kills my passive earnings. (maybe because of the A/C unit turning on?).
Bandwidth isn't an issue, but a stable/steady connection is very important. Basically, I have a small area with a high concentration of devices/modems and I want all of the devices to have a reliable connection (don't care about bandwidth). Is a signal booster right for me? Do I wrap the devices in foil?

Thanks!