About this replacement
TD Tech EP820 — 3.8V Li-ion Replacement Battery (BTY4000LI15)
This is a 3.8V Li-ion battery rated at 4000mAh (15.2Wh), built to the BTY4000LI15 specification. It fits the TD Tech EP820 two-way radio. Slide it into the EP820 battery bay and the radio's voltage-threshold bar indicator reads from the BMS directly.
- EP820 platform fit: The EP820 runs a single-cell 3.8V Li-ion rail with a proprietary BMS handshake on the battery contacts. This pack matches that voltage rail and contact layout, so the radio's protection circuit accepts it without a firmware flag.
- Bench tested on actual hardware: We cycled the BTY4000LI15 through transmit-load draws simulating PTT bursts. The BMS held the voltage rail steady across repeated high-current spikes and engaged overcurrent cutoff correctly at the threshold — no latching faults during normal PTT cycles.
- First-insertion contact check on the EP820 dock: If the charging dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The EP820 dock requires a clean contact cycle to complete the BMS handshake before charging starts.
Why the EP820 bar indicator reads low on a new BTY4000LI15
New Li-ion cells ship at storage voltage — typically around 3.6–3.7V — not at full charge. The EP820 uses a simple voltage-threshold bar indicator, so a cell sitting at storage voltage will display one or two bars even though the pack is not faulty. Put the battery through a full charge cycle in the dock before reading the bars. Once the cell reaches its rated 3.8V nominal operating point, the indicator will reflect the actual state of charge correctly.
EP820 cuts out mid-transmission on the BTY4000LI15
Transmitting on a two-way radio draws a high current spike the moment PTT is pressed — far above standby draw. If the battery contacts are dirty or slightly unseated, internal resistance spikes under that load and the BMS interprets it as an overcurrent event, cutting the radio off mid-transmission. Remove the pack, clean the gold contacts on both the battery and the radio with a dry cloth, and reseat until the latch clicks. If the cutout persists, charge the pack fully and confirm resting voltage is at or above 3.75V before field use.