About this replacement
Razer Viper Ultimate / Viper V2 Pro — 3.7V Li-Polymer Replacement Battery (US702428P)
This 3.7V, 500mAh Li-Polymer battery replaces the internal rechargeable cell in the Razer Viper Ultimate and Viper V2 Pro wireless gaming mice. It fits RC30-030501 and RZ01-0439 variants along with three additional confirmed models in that lineup. Swap it in when the original cell no longer holds a useful charge or fails to charge at all.
- Viper Ultimate and Viper V2 Pro platform fit: Both mice share the same battery bay geometry, connector orientation, and BMS handshake voltage. The US702428P cell works across the full platform without modification to the battery contacts or firmware.
- Bench tested on actual hardware: We ran this cell through the Viper Ultimate's charge circuit and confirmed the BMS accepted the cell without triggering a fault state. The charge IC ramped through pre-charge, constant current, and constant voltage phases cleanly.
- Li-Polymer storage voltage for wireless mice: If you're shelving the mouse for more than a few weeks, discharge the cell to around 3.7–3.8V before storing. Storing at full charge accelerates capacity fade in small-format Li-Polymer cells at this capacity range.
Why the Viper Ultimate's pointer stutters and polling rate drops before the battery reads empty
The Viper Ultimate's wireless receiver maintains a 1000Hz polling rate under normal voltage. Once cell voltage sags below roughly 3.5V under load, the mouse firmware throttles the polling rate to reduce current draw and extend operation. This shows up as intermittent pointer lag or micro-stutters that feel like interference but are actually a voltage-driven power saving response. The battery gauge may still show one or two bars because resting voltage recovers slightly when the mouse is idle.
Mouse not reconnecting to USB receiver after battery replacement
A full power loss during the swap clears the mouse's active pairing state in some firmware revisions. The USB receiver doesn't automatically re-establish the link because it's waiting for a handshake the mouse never sends after a cold start. Unplug the USB receiver, hold the pairing button on the bottom of the mouse for three seconds, then re-insert the receiver while the pairing LED is blinking. The mouse should reconnect at that point.