Sealite SL60 Replacement Battery 3.6V 8600mAh Ni-MH B8-3.6

Sealite SL60 / SL70 — 3.6V Ni-MH Replacement Battery (B8-3.6)

This is a 3.6V 8600mAh Ni-MH replacement battery for the Sealite SL60 and SL70 solar marine navigation lights. These lights run on buoys, channel markers, and coastal structures where the battery absorbs charge from the solar panel during the day and drives the LED through the night. When the original cell degrades, flash timing shortens or the light fails to complete its night cycle.

• SL60 and SL70 compatibility: Both models share the same battery bay geometry, connector pin-out, and 3.6V charging rail from the solar controller. The B8-3.6 cell fits either unit without modification.
• Bench tested on actual hardware: We cycled this cell through the SL60's solar charge controller and confirmed the BMS accepted charge correctly, reached full capacity, and maintained stable output voltage through a full discharge cycle without triggering a protection cutoff.
• Terminal maintenance before salt-season storage: Before storing the unit over winter or extended off-season periods, remove the battery and wipe all contact terminals with a dry cloth. Salt air deposits on terminals create resistance that slows solar charging even while the battery sits idle in storage.

Why the SL60 stops flashing before dawn

The SL60 solar controller draws from the battery at a fixed current to maintain flash timing. As a Ni-MH cell ages, internal resistance climbs and usable capacity drops faster than rated capacity suggests. The controller hits the low-voltage cutoff earlier in the night cycle, and the light goes dark hours before sunrise. A cell showing 8600mAh on paper but high internal resistance will fail this test every time. Replacing the cell restores full discharge headroom and consistent overnight operation.

Light activates during daylight after battery swap

After fitting a new battery, some SL60 units trigger the light during the day before the photo sensor re-calibrates to the new voltage reference. This happens because the light sensor threshold is set relative to the battery's resting voltage, and a fully charged fresh cell sits slightly higher than a degraded one. Power the unit down completely, leave it off for 60 seconds, then expose the panel to full daylight. The sensor re-calibrates at the correct threshold and daytime activation stops.