Synergy Digital GPS Battery, Works with Garmin Zumo 590LM GPS, (Li-ion, 3.7V, 1800mAh) Ultra High Capacity, Compatible with Garmin 010-12110-003, 361-00077-00, 616-00077-00 Battery - Walmart.com
Garmin Zumo 590LM vs Zumo 660, should you upgrade? - YouTube