My GPS uses 2x AA cells and I use Ikea LADDA 2450 NiMH cells. They are 6 years old and work brilliantly. One set will power the GPS for about 24hrs before needing a recharge.
Last weekend I had recharged 4x AA cells and put them in the SOTA box along with the GPS. I didn’t need the GPS for Friday’s walk so it stayed in the car. It was below zero rising to about 6C during the day. Overnight the temperature dropped to -5C. Bottles of water in the car did not freeze so the temperature in the car did not drop below zero.
Saturday morning I powered up the GPS whilst getting ready mainly to record the route. When I came to set off there was no display. I repowered the GPS and it worked for about 1min before shutting down. I swapped to the other batteries and stood about for 5mins or so and the GPS was fine. This happened once before in December 2024, GPS would not stayed powered and swapping cells fixed the issue.
My thought was one or both cells cannot provide current when cold. I placed both cells in a LED torch that draws 45mA and it stayed powered for 39hrs in the shack (14-20C). After this use the cell voltages are 1.23 and 1.24V. Maybe it was the cold. I placed both cells in the deep freeze (-16C) for 1hr and tried and the GPS powered up and stayed powered. The GPS pulls around 100-120mA without backlight.
A new pack is only £6 and I have 6 more LADDA cells that work so I may just drop these into the recycling centre. It probably makes more sense not to have dodgy cells in the SOTA box.
My main question is just what is failing? The cells work fine now at 45 or 100mA load and fine when damn cold. But this is twice batteries left in the car overnight in Winter have failed. That’s once too often!
I’m not using NiMH cells anymore, having changed to Alkaline in the GPS and LiFePO4 batteries for my TX-500 or KX3 when doing SOTA. Even so I carry the GPS and the LiFePO4 batteries under my anorak in the pockets of my fleece jacket to keep them warm
So the batteries which failed when they had been to near 0C didn’t work. I think internal resistance could be a failure mode. But other identical batteries stored in the same conditions work fine. Then the batteries that failed when cooled well below 0C (towards -16C) still work. There is something else I think.
I activated Place Fell in full winter conditions, I estimated -10C but it might have been lower. The 817 started off normally but faded quickly and died on me. Later in the climbing hut the batteries recovered and worked normally. These were 2500mAh NiMH. Whatever happens takes time, I doubt that a solution of KOH freezes at such temperatures, it is some form of gradual passivation over time. Whatever the mechanism, it is something that is recognised and NiMH batteries that work reliably below 0C are available.
I agree with Brian. Old batteries already have higher internal resistance and lower capacity. Cold weather compounds these issues, making an old battery behave like a dead battery. At freezing or near-freezing temperatures, NiMH batteries can lose 20% to 50% of their effective capacity. Cold temperatures make ions move slower and cause the electrolyte to become viscous. This creates high internal resistance, meaning the battery cannot deliver power quickly, even if it is technically charged.
Without knowing the history and usage of your other batteries, it’s impossible to answer why they differed.
One possibility is one of the batteries is partially defective (did you measure their emf individually?) and is dragging down the capacity of its neighbours.
If you’ve used them regularly for 6 years, they don’t owe you anything. Perhaps it’s time to prise open the sporran and buy a new set to avoid on-summit disappointment.
Are the hybrid cells any better for this? I bought Ikea Ladda 1900mAh cells instead of the higher capacity ones so I can have them all charged up and ready to use and not worry about them self-discharging.
I’ve found the self-discharge of Ikea’s LADDA cells to be very low. The cells here were all fully charged in Ikea’s Vinninge charger last September 29th, that’s when I drove up for a SOTA-dxpedition to the Scoraig Peninsula (NS-117, NS-100 & NS-080). That’s a 220mA charger with timed and -dV shutdown. The cells that failed shortly after switched on have been charged once since then. I pulled some others out of the big box of SOTA stuff and checked the voltage… each cell showed 1.309 & 1.307V and putting them in the GPS, it showed 4 blobs, i.e. full charge. So that’s 5.5months self-discharge and they seem to be very well charged still.
I put the two suspect ones on charge this morning and took the dog out ‘dogging’. When I came back the charge light was flashing which means fault. I’ve seen this when the two cells don’t charge at the same rate and one was at 1.2 and the other 1.32V. Putting them in 2 chargers, 1 to each charger, they both charged up happily.
So it looks like one charges slower than the other… maybe it needs “frightening” back to life. i.e. shocked with a high current pulse to melt any dendrites that may have formed in the charge/discharge cycles. Actually I’ll mark the pair as suspect and treat myself to a new pack from Ikea in Edinburgh as they’re £8 for 4. It also means I can buy some Huvudroll as well. It’s years since I had any and maybe they don’t taste the same now there’s no horsemeat in them ? My lad was 8 when I first bought some. Now he’s early 30s, getting married and has a daughter. Tempus fugit
I agree that a flashing fault light when charging two old, deeply-discharged NiMH batteries together is almost certainly caused by the charger detecting that one or the batteries is defective or heavily degraded, leading to an imbalance in their charging rates.
Rather than trying to “frighten” the terminally-ill patient “back to life” it might be more prudent to give it an environmentally-safe disposal. The ‘sick’ one might well charge up on its own but this is misleading and - as discussed above - that doesn’t mean it has the capacity, charge retention, discharge rate (under load), cycle life and temperature tolerance of a new or new-ish one.
I placed both cells in the deep freeze (-16C) for 1hr and tried and the GPS powered up and stayed powered. The GPS pulls around 100-120mA without backlight.
Reading the description I would say that GPS is the problem,not the cells.
However, battery life is limited to 5 years or less …
Expected battery life is two to five years
So you might be trying to use aged-out batteries at low temperature, and tipping them over a cliff.
New NiMH batteries work very nicely - we often use batteries which are >2-5 years old, and when new, they were quite a lot less capacity than today’s replacement NiMH . Unsurprisingly, they seem poor.
My money would go on this not being a battery issue. Presumably the battery compartment in the GPS has a metal spring contact on one end and a metal tab on the other for each battery. The contact between this type of battery and the spring contact is a potential high resistance point. I have experienced this with my GPS. The act of swapping out the batteries cleans up the contact and hey presto, no more problem.
This is the same issue that we get with our TV remotes. Often one or the other won’t work and a simple tap of the remote on a hard surface is sufficient to remake the contact between the spring and the battery.
When I ran a FT-857 for SOTA, I used a high capacity NIMH in series with a 3S LIPO to provide sufficient voltage for the rig. I would have preferred to use LiFePO4s, but they were very expensive at the time. I often had issues with the set up until I modified the NiMH holders and put pieces of copper on the ends of the spring contacts. This increased the contact area with the battery so overcoming the problem.
A few weeks ago I realised that my FT817ND was not lasting as long as it used to per charge, so I checked the batteries, and four of them were down to about 40% of capacity so I treated the rig to a new set. It only gets used for monitoring nowadays (and an occasional chase on 60m) but I intend to take it on holiday in a few months time. Incidentally, the old batteries were bought in 2011!
I used the same IKEA LADDA batteries in my FT-817. I realised that at low temperatures, the FT-817 reduced the output power to 2.5W, due to increased internal resistance. Capacity was still ok for activations of 1 hour+ in this case.
With brand new batteries, the “low” temperatures that triggered the power reduction were below 0°C. With increasing age, this “low” temperature increased,and at the age of 3, it was around +10 to +15°C. That’s where I swapped the batteries for the TRX and used them for something else.
I had a little retail therapy in Ikea today, new LADDAs purchased along with lots of other stuff. That always happens when I visit there
Best was when I was looking at kids toys… my ‘new’ grand-daughter is 9 months old and I was seeing what things they may have. I was stunned that on two occasions (two different soft toy sections) women came up and started talking to me. Hitting on me? Who knows. Maybe it was just the site of an old bloke with a strong resemblance to George Clooney looking at toys for very young children that triggered them. A nice surprise but sadly both ladies were my age group and not 20-40 years younger (They were very nice ladies but not Bond Girls!) I told Mrs. LLD and she suggested I should check my blood sugars and asked me if I’d suffered a blow to the head recently. That deflated me suitably.
Thanks for all the suggestions and comments. The new cells are a different colour so easy to distinguish from the old cells.
My lad was 8 when I first bought some. Now he’s early 30s, getting married and has a daughter. Tempus fugit 
(They were very nice ladies but not Bond Girls!) I told Mrs. LLD and she suggested I should check my blood sugars and asked me if I’d suffered a blow to the head recently. That deflated me suitably.