Lithium and alkaline battery cold testing
Amongst the various journeys, fact-finding missions and equipment assessments that have punctuated my 2017 winter in the High Arctic territory of Svalbard, I have also turned my attention to the minutiae of what it takes to live and travel successfully this part of the world.
So much that matters today, like it or not, even on the ice, requires power. Satellite communications, navigation, filming, and in the dark, torches, are indispensable parts of modern remote travel in the cold.
Instead of having a mess of different battery types, charging systems and the weight they represent, it makes sense to use a single ‘base source’ of power. Having considered the different sizes, chemistries and options on the market, I have found that typical AA batteries are excellent in this role. They can be used solo in units like GPS handsets, or combined in power packs to create 12V that all sorts of tech can charge from. Some are rechargeable, but the NiMH chemistry used for these (even the newer low-self-discharge types) is notoriously impotent once the mercury heads south of zero.
I’ve run some tests of a few common AA cells – so a geek alert I’m afraid – but have tried to cut to the useful information pretty quickly.
I tried two traditional alkaline types, GP Ultra (a well-regarded budget brand) and Duracell (their standard cell), and two lithium AAs, again from GP, and the pricier market leader, Energizer Ultimate.
Lithiums are well known to be better in the cold, especially under high load, so there will be little surprise in the results alkaline vs lithium, but the question is by how much? Is the major price difference worth it? And how much to they vary between brand?
So, here’s what I found:
The alkalines had a voltage of around 1.6V without a load. For batteries listed as 1.5V (typical for single use AAs – 1.2V is more normal for rechargeables) this is about right. Once loaded (I used a 0.3A lightbulb per cell) this dropped to 1.5V. Having chilled the whole system down to just below -20 degrees C, it read 1.35V. Then, I let them discharge through the bulbs. After just 20 minutes the Duracells were at 1.1V, and 1.0V after forty minutes. The GP Ultras fared better at 1.2V and 1.1V. AA performance at a volt becomes very poor, and some would say a voltage sub-1.2V is not useful. It is worth saying that a larger drain (from a powerful torch) reduces a battery’s useful capacity (the mAh number) and so are often quoted at currents like 0.05A in order to sound better. The GPs held out until 0.9V at one hour, whilst the Duracells failed to light the bulb at this point. The batteries were re-warmed and gave a voltage of around 1.14V (Durcell) and 1.37V (GP Ultra). They were dead, and nearly dead.
The lithiums had an unloaded voltage of 1.8V (Energizer) and 1.9V (GP). Loaded, these dropped to 1.5V and 1.6V. In the cold, these only dropped around 0.05V, which is impressive. From this point, the batteries were left to discharge, with the Energizer holding a higher voltage when tested each hour. After one hour, it was 1.33V, two hours, 1.32V, and four, 1.30V. The GP’s results were 1.27V, then oddly, 1.30V for the two and four hour checks. After eleven hours, the Energizer was holding on at 1.07V with a dim glow in the bulb. The GP was dead. On rewarming, both returned to around 1.5V unloaded. An oddity I noticed, and have done so when using two GP cells in a GPS, is that occasionally after heavy use the cell will read 0.0V – it dies entirely. Whether this is because in series current is being drawn unequally and ‘toasts’ one cell entirely, I don’t know. Energizers don’t tend to do this so dramatically.
So, with plenty more testing yet to do, the results as I see them are:
In the cold, forget alkalines. Simple. If you have an excellent recharging system, perhaps LSD-NiMH (like Eneloops) have a use, but they will need constant care. The very afforable GP Ultras beat the Duracells fair and square, even if neither performances were stellar.
For serious low temperature use, lithiums are the solution. Sadly, rechargeable Li-Ion or Lithium polymer AAs are not available. You could buy readymade 12V Li-Ion power packs and charge units from that, but the weight and cost per Ah is higher than AAs, and you’d need to recharge the power pack itself in the warm.
If using lithium AAs (very few brands are available), both perform excellently in the cold – they leave the alkalines trailing far behind in a way they wouldn’t with moderate loads in the warm. They are also a quarter to a third lighter in weight. The ~20% price saving of the GPs over Energizer might be enough to swing your vote, even given the slightly odd behaviour I found. A critical takeaway is to get a proper multimeter – and one of those £5 mini-testers as a bare minimum. You’ll avoid throwing away good batteries when only one in a handset has actually gone flat. You can also identify faulty cells, and find out where problems are in your DIY charging rigs etc.
There you have it – buy quality batteries if you’re off somewhere cold.