diff --git a/CONTEXT.md b/CONTEXT.md
index 1bb1df6..ba2097b 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -56,6 +56,13 @@ Digital + checksums = bad signal just means slower transmission, not errors.
 |------|---------|
 | SDRplay RSP1A | View TX signal, debug, spectrum analysis |
 
+### Power (Relay Node)
+
+- Milwaukee M12 3.0Ah battery (~$30, adapter plate ~$5)
+- 3S Li-ion, 11.1V nominal
+- ~0.17Ah/day (5mA idle + TX bursts)
+- Runtime: ~2.5 weeks on single charge
+
 ### Antenna Options
 
 **Earth Electrodes (best range):**