Electric Car Batteries - How Well Do They Perform In Cold Climates?

By Carmel M.d Morris

Electric Car Batteries - How Well Do They Perform In Cold Climates?. For many electric car enthusiasts, the budget will only allow for deep cycle Sealed Lead Acid (SLA) batteries. Anyone driving such cars will know that lead acid batteries can be somewhat sluggish in cold climates, just as a regular cranking battery can be in a gas vehicle.

Typically, CCA (Cold-Cranking Amperage) of a regular car battery is the amount of current a battery is capable of delivering for 30 seconds at zero degrees Fahrenheit without dropping below a specified cutoff voltage (which for cranking batteries is anywhere from 9.5 - 11.5 depending on manufacturer). This value typically changes as temperature changes. As the weather gets colder, the level of amp hours is reduced.

For an electric vehicle, SLA batteries are not manufactured to be cranking batteries yet their efficiency is still affected in cold climates, particularly if not charged to capacity. Note that cranking batteries are not used in electric vehicles due to their lack of repeated discharge/recharge capabilities. The plates are typically thin with paper separators whereas SLA batteries have thicker metal plates.



A typical optimal operating efficiency for a SLA is around 77 degrees Fahrenheit. Any colder or warmer and the battery is less efficient. Although a battery's charge state may not vary greatly, access to that charge, namely 'voltage sag' is affected. Higher temperatures mean increased current use. Ambient temperatures also affect batteries in storage. Higher temperatures accelerate discharge.

Are lithium batteries any better at handling temperature variations?

Despite the advent of new more energy-dense lithium batteries, the promise of high performance in all temperatures can still be tested when it comes to the amount of voltage currently stored in the battery. Since refined lithium phosphate chemistry is relatively new on the battery scene, access to accurate laboratory tests has been difficult to obtain.

This article would be very long if I were to go into all the details about battery comparison in cold climates. Suffice to say that lithium chemistry will still get your electric car going more efficiently than a SLA of similar specification. Nickel Metal Hydride (NiMh) batteries are less able to tolerate colder temperatures and elaborate insulation technology is used in some new vehicles being developed with such batteries.

As for my lithium phosphates, the energy delivery for regular driving conditions is slightly less than for lithium cobalts (3C instead of 4C approximate (three times the rated Ah)) and that capacity is not adversely affected with moderate temperature swings in either direction.

I do not notice any decline in performance at 46 degrees Fahrenheit which is a typical winters day in my location.

If you're serious about checking the performance of your own batteries, contact your manufacturer. With the increasing popularity of lithium batteries, more data sheets are becoming available now for electric car enthusiasts (and I intend to get the latest data from my supplier too when their documents are updated).

For a typical 100Ah lithium phosphate battery, the basic specification is quite impressive;

Voltage: 2.5 - 4.25V
Operating Temperature: -25C to 75C

Some electric vehicle owners give their packs a quick top-up charge before they leave home (providing the vehicle is fully-charged from the night before) and they say this compensates for any lag in performance on a cold morning.

Typical for most batteries, while battery capacity may be greater at a higher temperature, battery cycle life (the number of times it can be charged and discharged) is shortened. Conversely, battery capacity reduces by as much as 65% at minus 25 degrees Fahrenheit, yet cycle life rises by roughly the same amount.

Protecting lithium battery packs in varying climates

There are some options I have considered for protecting battery packs in warmer climates such as devising coolant ribbing in gel-packs, the circulation driven by a 12v motor with a PC-style radiator and coolant bottle (a similar setup I have already installed for my motor controller underside cooling block). An option for colder climates would be to employ one of those 12 volt engine bay warmers available for cars in snowy regions. These circulate warm water to heat the engine block. In my case I would route the warm water through the same kind of gel pack membrane. A switch over or logic-controlled temperature sensor can handle automatic cooling and heating no matter where you are, keeping batteries at their optimal operating temperatures.

Some may tell me this idea will use battery resources and driving distance would be reduced (since power from the pack is used to thermally protect itself). For my kind of driving (40 miles a day), I'd be happy to reduce range by four percent or so if it greatly improves the life of my batteries.