Short answer: most UPS failures during a power cut are battery failures. Check batteries every quarter, keep them cool, and replace weak cells before they pull down the whole bank.
Why batteries fail without warning
A UPS battery bank is a chain of cells in series. One weak cell lowers the whole bank's backup, but on normal mains the UPS shows nothing wrong. The problem appears only when the power goes – exactly when you need it.
Quarterly checklist
- Inspect for swelling, leakage, cracks and corrosion on terminals
- Check terminal tightness and clean connections
- Measure individual cell/block voltage and the total bank voltage
- Compare readings – one block noticeably lower than the rest is the early warning
- Note room temperature; heat shortens battery life sharply
- Run a controlled backup test where the load allows
Tubular vs SMF: maintenance differences
Tubular batteries need electrolyte level checks and topping up with distilled water. SMF (sealed maintenance-free) batteries need no topping, but still need voltage and temperature checks.
When to replace
Replace when backup time has dropped noticeably, blocks show physical damage, or individual block voltages drift apart under test. Replacing the full bank together usually gives more consistent results than mixing old and new blocks.
Unitech's battery maintenance contracts cover this testing on a schedule. See tubular and SMF batteries.