Is lithium always the better choice now?

No. On pure standby duty in a cooled room, with a few outages a month, a VRLA or OPzV string delivers the required autonomy for less money over the same period. Lithium wins on daily cycling, warm rooms, weight and floor space.

Can I mix chemistries in one system?

Not within a string, and not in parallel without a controlled design. Charge voltages, temperature compensation and end of discharge limits differ, so the weaker chemistry is damaged. Parallel strings of different chemistries require separate charge control.

What does AGM versus GEL change?

AGM holds electrolyte in a glass mat, has lower internal resistance and suits short high current discharges such as UPS. GEL immobilises electrolyte in silica, tolerates heat and cycling better, and suits solar and longer discharges.

How do I know what my current system actually delivers?

Only a capacity discharge test proves delivered capacity against the rated value. Impedance trending finds weak cells between tests. EXBATT performs both, including on systems supplied by others.

All insightsInsight

Battery chemistries compared

6 min readLast reviewed: September 2026

Short answer

For standby duty at stable temperature, AGM and GEL VRLA batteries remain the lowest first cost, with 5 to 12 years of design life. For long life standby, OPzS and OPzV reach 15 to 20 years. For daily cycling, warm rooms or tight floor space, lithium iron phosphate wins on cost per usable kWh despite a higher purchase price, because it delivers thousands of deep cycles and tolerates higher temperature.

Most specification arguments are really one question: which chemistry suits this duty cycle, this room and this replacement budget. This is the comparison we use internally, with the figures that actually decide the outcome.

The comparison table

Figures are typical for correctly installed systems at 20 degrees Celsius. Design life is the manufacturer figure for standby float duty. Cycle life is to 80 percent of rated capacity at the stated depth of discharge. Read them as selection guidance, not as a warranty.

Typical characteristics by chemistry
Chemistry	Design life	Cycles	Usable depth	Temperature	Best duty
VRLA AGM	5 to 12 years	200 to 500	50 percent	Sensitive above 25 C	UPS and telecom standby
VRLA GEL	8 to 15 years	500 to 1200	50 to 60 percent	More tolerant than AGM	Solar and cyclic standby
OPzV (gel tubular)	15 to 20 years	1200 to 1800	60 percent	Good	Long life standby, no maintenance
OPzS (flooded tubular)	18 to 20 years	1500 to 2500	60 to 70 percent	Good, needs ventilation	Substations, hydro, harsh sites
Lithium iron phosphate	10 to 15 years	3000 to 6000	80 to 90 percent	Tolerant to 40 C	Daily cycling, BESS, tight space
Nickel cadmium	15 to 20 years	2000 to 3000	80 percent	Minus 20 to 50 C	Extreme temperature, rail, genset start

Read cost per usable kWh, not price per battery

A 100 Ah VRLA battery and a 100 Ah lithium module do not deliver the same energy. Lead acid is normally limited to 50 percent depth of discharge to protect life, so half the nameplate is inaccessible. Lithium is routinely used to 80 or 90 percent. Divide the purchase price by the usable energy, then by the number of cycles or years the duty will actually demand. On standby duty with two or three outages a month, lead acid usually still wins. On daily cycling, lithium wins by a wide margin.

Temperature decides more than the datasheet suggests

Lead acid service life roughly halves for every 10 degrees Celsius above 20. A VRLA string rated for 10 years in a room that sits at 30 degrees through the summer is a 5 year string, and the replacement cost arrives twice as often. Either cool the room or select a chemistry that tolerates the real ambient. In unconditioned containers, cabinets on rooftops and small telecom shelters in Kosova and Albania, this single factor changes the answer more often than any other.

How we choose in practice

We start from duty cycle, then ambient temperature, then autonomy, then footprint and floor loading, and only then from price. Standby UPS in a cooled room: AGM or GEL. Substation DC with a 20 year asset horizon: OPzS or OPzV. Telecom shelter without cooling: lithium. Peak shaving or self consumption with a daily cycle: lithium. Genset starting or minus 20 degree sites: nickel cadmium. EXBATT is accountable for the selection and for what it does over its life, and we work with established manufacturers so the choice follows the case rather than a catalogue.

Frequently asked

Is lithium always the better choice now?: No. On pure standby duty in a cooled room, with a few outages a month, a VRLA or OPzV string delivers the required autonomy for less money over the same period. Lithium wins on daily cycling, warm rooms, weight and floor space.
Can I mix chemistries in one system?: Not within a string, and not in parallel without a controlled design. Charge voltages, temperature compensation and end of discharge limits differ, so the weaker chemistry is damaged. Parallel strings of different chemistries require separate charge control.
What does AGM versus GEL change?: AGM holds electrolyte in a glass mat, has lower internal resistance and suits short high current discharges such as UPS. GEL immobilises electrolyte in silica, tolerates heat and cycling better, and suits solar and longer discharges.
How do I know what my current system actually delivers?: Only a capacity discharge test proves delivered capacity against the rated value. Impedance trending finds weak cells between tests. EXBATT performs both, including on systems supplied by others.