I like my Garmin GPSMAP 64s. You can set it so it won't recalculate. It uses AA batteries and has good battery life. I use eneloop rechargeable batteries and can carry spares if I think I'll need them and can also buy a set of alkaline batteries at a store. It has buttons not touch screen which I like better as they work good in the rain and with gloves on.

If you would rather have a touch screen I think Garmin has touch screen units that also use AA batteries and the ability to disable recalculation.

I also have an eTrex 20 and don't like it for brevets as it will recalculate and there is no way to disable it. If you go off route say on a side street or even do a U turn to stop at a store or restaurant it will recalculate. Then when you are back on route it will recalculate again and this may or may not be the route you started with. Also if it's recalculating and you make another turn or U turn it will sometimes freeze up. You then need to power it down and sometimes if it's a bad freeze up remove the batteries.