I would say you need to check the battery specs. inside the Rockwheel. I believe the battery inside is the only difference.
The GR16-25R has a battery that the Mfg. refers in its specs. as “296Wh/ 32pcs”, whereas the GR16-20R has a little less battery-life and is referred to as “236.8Wh/ 32pcs.”
Hope this helps. I am looking for a replacement battery currently. tyanceyATemtrainDOTcom
Ty
On 2018-09-15ish