Page 8 - Understanding energy storage batteries

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Battery Operating Temperatures

A lot of battery testing is done in factories, at temperatures of
25°C. When batteries are used at higher or lower temperatures
the allowed DOD and number of cycles will reduce. This is
particularly relevant for lead acid and lithium-ion technologies.
For example a lead acid battery being operated at 30°C will have
its life reduced by up to half compared to if it is operated at
20°C. The lifetime will be reduced by half again if a lead acid
battery is operated at 40°C.

With many lithium batteries the warranties depend on batteries
being kept within certain ranges often a minimum of 5 – 10 °C
and a maximum of 35 – 40 °C. Lithium-ion batteries operating outside the recommended range will degrade or
not operate at all.

Most batteries achieve optimum service life if used at 20°C (68°F) or slightly below.

If, for example, a battery operates at 30°C (86°F) instead of a more moderate lower
room temperature, the cycle life is reduced by 20 percent. At 40°C (104°F), the loss
jumps to a whopping 40 percent, and if charged and discharged at 45°C (113°F),

the cycle life is only half of what can be expected if used at 20°C (68°F)

At –20°C (–4°F) most batteries stop functioning. Although NiCad can go down to –

40°C (-40°F), the permissible discharge is only 0.2C (5-hour rate), Specialty Li-ion
can operate at this temperature, but only at a reduced discharge rate; charging at
this temperature is out of question. With lead acid there is the danger of the

electrolyte freezing, which can crack the enclosure. Lead acid freezes more easily
with a low charge when the specific gravity of the electrolyte is more like water
Cycles
than when fully charged.

The more you discharge a battery (high DOD), the fewer cycles you get out of the battery with a reduced
lifetime of the battery. Larger batteries, like the SoNick battery are likely to have a lower DOD on a daily basis,
so are likely to last longer, while smaller batteries like the lithium-ion batteries are more likely to discharge
completely on a daily basis, thus reducing their overall lifetime.

Degradation

Many batteries will degrade over their lifetime which means you may need to install more capacity than you
would need upfront to allow for this degradation. Lithium-ion batteries can degrade down to 50 – 60% capacity
over 10 years while lead acid may degrade even lower to 30-50% depending on their operating condition.
SoNick and Redflow batteries don’t degrade so will remain at 100% capacity over their lifetime. This
degradation means you may not be able to add extra capacity to an existing system after a couple of years.

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