>>280192106
4 hours is the max, yep, they used a small battery for weight.
If they made trackers without the pogo connector and shit they could be much smaller, weigh less and have more battery life, but they weren't designed for this alone. It's sad that we're stuck with them and nobody wants to step up to the plate and make their own. HTC is currently operating a monopoly. 
HiveTrackers are the only alternative and you can't buy those fully assembled and working.
you can fully charge a tracker with a smallish battery pack several times though, generally. They do charge fairly fast. I usually just take a seat for a bit or just turn them off and allow them to charge up in 20 minutes.
It's very rare that sessions in vrc go over 18 hours. 
With a battery pack attached, even a small one, you can get 18-24 hours out of them I've heard.