About this replacement
VOLVO C40 / S60 / S90 Series — 8V HPC Replacement Battery (31450445)
This is an 8V, 640mAh HPC replacement battery for the VOLVO vehicle siren alarm system. It fits the C40, S60, S60 MK3, S90, and over 46 additional models. OEM part numbers 31450445, AC15, and P0839A all cross-reference this battery.
- Cross-model fitment across VOLVO platforms: These models share the same siren alarm housing, connector, and 8V activation threshold. The BMS handshake is consistent across this family, so one battery specification covers the full range without modification.
- Bench tested on actual hardware: We cycled this battery through siren activation loads and monitored the BMS cutoff behaviour. The cell held voltage within spec across repeated short-duration discharge bursts, and the BMS did not trigger premature cutoff under simulated alarm output current.
- Siren cover and tamper switch check after install: After fitting this battery, close the siren housing fully and confirm the tamper switch is physically engaged. VOLVO alarm sirens with an unseated tamper switch report a fault condition that some alarm panels misread as a battery error — the battery is fine, the cover latch is the cause.
Why VOLVO siren batteries drain between annual alarm tests
The siren sits in the engine bay or wheel arch area, exposed to wide temperature swings year-round. HPC cells in this environment self-discharge faster than bench figures suggest — heat accelerates the process significantly. A battery that tests fine in summer may arrive at the annual test depleted in winter. Fitting a fresh battery within six weeks of the scheduled alarm test is the straightforward fix.
Siren sounds briefly then cuts out during alarm activation
This symptom points to a battery that cannot sustain the current draw needed to keep the sounder active for a full alarm cycle. The siren draws a short burst of current at activation — if the cell voltage sags below the siren's minimum operating threshold mid-cycle, the sounder cuts out. A depleted or aged battery will pass a resting voltage check but collapse under load. Measure cell voltage under a light load: if it drops below 6.5V, replace the battery.