UPS batteries

A UPS is only as reliable as the batteries behind it. This section lists the 6 V and 12 V VRLA AGM blocks used in uninterruptible power supplies for offices, racks and data rooms, from brands such as LONG, RITAR, Q-BATTERY and FULBAT.

Search by capacity, size and terminal and swap the worn block for a matching one.

How a battery works inside a UPS

For months it sits on float doing nothing you can see. When the mains fails, the UPS inverter draws on it instantly to keep the load running for a few minutes: long enough for a generator to start or for servers to shut down cleanly. That is a short, heavy discharge, very different from the slow draw of a solar system.

Values to copy from the old battery

• Voltage and capacity: the most common sizes are 12 V 7 Ah, 9 Ah, 12 Ah and 18 Ah, while large UPS units take blocks from 40 to 200 Ah.
• Dimensions: battery bays leave no slack, so match length, width and height including terminals.
• Terminal: F1 (4.8 mm faston) and F2 (6.3 mm faston) on small blocks; M5, M6 or M8 bolts on bigger ones.

A slightly higher capacity in the same case gives more runtime, provided the voltage matches and the block fits.

Service life and when to replace

Standard series usually carry a 3–5 year design life and long-life series (the WPL range from LONG, for example) up to 10–12 years, always rated at 20 °C. A UPS in a hot cabinet ages them faster. Warning signs are shorter runtime, a failed self-test or a swollen case. On multi-block units, change the full set with units of the same date code.

If your load needs high power for just a few minutes, look at high-rate UPS batteries. For other standby uses, go back to stationary batteries.

Common questions when replacing UPS batteries

Do I need to switch the UPS off?

It depends on the model: some support hot-swap and some do not. Follow the maker's manual and, once the new blocks are in, let the UPS charge for several hours before running a calibration or self-test.

Can I mix brands in one UPS?

Better not. Even with identical labels, internal resistance differs between manufacturers and the weakest block ends up limiting the runtime of the whole string.

What should I do with the old batteries?

They are lead waste and belong at an authorised collection point. Never put them in household rubbish.