Note the presence of hazardous materials and conditions that must be approached with proper precautions and procedures to avoid damaging, injurious, or even fatal consequences.
It is relatively easy to turn a Prius into a well-performing pure EV.
One would start with a 2004+ Prius with a worn-out or destroyed engine, but intact transaxle. Remove the engine and gear the transaxle's engine input shaft to the output shaft, possibly with a cogbelt. This is to turn the engine input shaft at a speed (e.g. 500 rpm @ 60 miles per hour or 97 km/h) that prevents MG1 from overspeeding when driving at highway speeds (above 62 miles per hour or 100 km/h ) while making MG1's output power available to help drive and stop the vehicle.
With MG2 rated at 50 kW output and MG1 rated at at least 25 kW, one could potentially provide up to 75 kW to the wheels for acceleration as an EV, only slightly less than the 82 kW peak available as a hybrid. One could remove the 21 kW DC:DC converter between the battery and motors, and instead provide a battery pack with a peak charging voltage of 500V. The motors and high power drive electronics could be used as is. It would hopefully be possible to bypass all the hybrid system logic and use only the motor driver circuits; otherwise, they would have to be replaced.
Electrovaya makes a 48V Li-ion module that stores 1.6 kWh and weighs 9.5 kg (21 lb). A 1P9S/2P9S/3P9S, 433V, pack would hold 11.4/23.0/34.6 kWh to 80% DOD and weigh 188/376/564 lb. One of these packs would add just -112/76/264 lb to the vehicle after removal of an estimated 300 lb of OEM battery, engine, and related components -- and would provide an estimated 57/115/170 miles of EV range. The battery cost, however, would be US$17k/$35k/$52k at an estimated $1200 per kWh-capacity.
A 1P33S pack of 12V, 30Ah Gold Peak NiMH modules would add 324 lb to the vehicle's weight, store 9.5 kWh to 80% DOD and weight 624 lb. It would add 324 lb and would provide an estimated 48 miles of EV range. At an estimated $1200 per kWh-capacity, the pack would cost $14.3k
In contrast, fuel savings at $0.10/kWh vs. $4.50/gallon would be $0.075/mile or only $11k over 150,000 miles at today's prices, well below the cost of even the 48 EV mile battery pack.