{"product_id":"tetra-cassidian-thr9-replacement-battery-37v-5700mah-li-ion","title":"BLN-5i TETRA CASSIDIAN THR9 Compatible Battery 3.7V 5700mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eTETRA CASSIDIAN THR9 — 3.7V Li-ion Replacement Battery (BLN-5i)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.7V, 5700mAh Li-ion replacement battery for the Cassidian THR9 TETRA portable radio. It also fits the HT9588AA and HR8509AA variants. OEM part numbers covered: BLN-5i, BLN-6, and BLN-Ex-2 U.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eTHR9 platform compatibility:\u003c\/strong\u003e\n    The THR9, HT9588AA, and HR8509AA share the same battery bay geometry, contact layout, and BMS handshake protocol. All three accept this pack without modification to the door latch or contact rail.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled this pack through the THR9 charger dock and monitored BMS response through transmit current spikes. The protection circuit handled the sustained RF output load without tripping, and the dock progressed through its charge stages correctly.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFirst-insertion contact cycle on the THR9 dock:\u003c\/strong\u003e\n    If the dock shows a fault LED on first insertion, remove the battery and wipe the gold contact strip with a dry cloth before reseating. The THR9 charger requires a clean contact cycle to complete the BMS handshake before it will begin charging.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the THR9 cuts out mid-transmission on a new BLN-5i\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe THR9 draws a sharp current spike the moment PTT is pressed — transmit load is significantly higher than standby draw. If the BMS reads that spike as an overcurrent event, it trips the protection circuit and kills output mid-call. This usually happens when the cell is at storage voltage, not fully charged, and internal resistance is temporarily elevated. Charge the pack fully in the dock before first field use and the BMS will handle PTT spikes without tripping.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eBar indicator showing one fewer bar than expected on a fresh BLN-5i pack\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThe THR9 reads voltage thresholds to display its bar indicator — it does not use a fuel gauge chip. A new cell ships at storage voltage, typically around 3.6–3.7V, which the radio reads as a partial charge state. This is normal and not a fault with the pack. Run one full charge cycle in the dock and the indicator will reflect the actual 5700mAh capacity correctly.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43426299019354,"sku":"BWCS-ETH920TW-1","price":45.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43426299052122,"sku":"BWCS-ETH920TW-2","price":53.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43426299084890,"sku":"BWCS-ETH920TW-3","price":59.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-ETH920TW-1.webp?v=1779930583","url":"https:\/\/batteryweb.com\/products\/tetra-cassidian-thr9-replacement-battery-37v-5700mah-li-ion","provider":"BatteryWeb","version":"1.0","type":"link"}