Smallest wired tracker with backup battery
I've occasionally added a second "trailer brake" battery box and stuffed a tracker and a trailer brake battery in it. As for the tracker, we use Teltonika ourselves, and a Teltonika FTC880 has a 320mA battery and is IP69K rated. If you make it go into ultra deep sleep when not being towed, that 320mA would last about 106 hours, even if there was no battery on the trailer.
Generally for trailers though, I provide my customers with the Teltonika TAT240. 3-5 year battery, but only if it checks in a couple times a day. It has a tamper detection mode though that if it gets removed it goes into "recovery" mode and checks in every 3 minutes. It also has multi-cell LBS detection so it can give you its location via GPS or cell tower data.
I want to track my trailer but it only has power when I'm towing it with my truck. When the truck electric wire is unplugged from the trailer, the backup battery must be used for tracking. I will be splicing one of the trailer wires and attaching it so it stays hidden.
The smallest I've found so far is SinoTrack ST-907 but the battery is very small and barely lasts. Is there any other tracker that is small, hard wired, with battery that lasts at least a couple of days?