A couple of months ago I ordered several Bioenno batteries of various sizes, probably spending more than I need but felt the need to justify the ridiculous shipping charges from US to Isle of Man. Since then I’ve been wondering how to best discharge them to their recommended storage capacity of 50% - 60% given that voltage is not a reliable indicator due to their discharge profile.
I’m happy now that I’ve found a solution: an inline wattmeter (clean Amazon link) to measure power used:
As soon as you connect this to the battery it lights up with voltage and current being drawn, and maintains a counter for, amongst other things, Ah and Wh. So I either bring it with me on an activation and note down the amount of power used each time, or connect a freshly charged battery to a load and count down to about 50%, so roughly 18 Wh for my smallest 36 Wh battery.
But which load to use? I couldn’t resist hooking up my IC-7300 earlier today for what was intended to be a spot of listening, but N1W was very strong with me so I gave in and got a 59 across the pond at 1W of RF, hehe. Knew there was a point to WWA after all.
I have one of those meters as well - works pretty well. Not sure what field rig you are using, but the KX2 can keep track of how much power has been consumed from the battery. You just have to remember to zero it out before you start your activation!
Absolutely; there’s a backlight and some electronics in there, so of course it’ll drain the battery very slowly when connected, though not enough to be used as an effective load in it’s own right. Interestingly it doesn’t display any current being drawn by itself, but I expect that it’s due to the meter’s 2 decimal places not offering enough precision for such a small drain. Maybe I’ll leave it connected for a couple of days in order to see if the total drained increases at all.
Oh hey, that’s neat! My Icom ID-705 only shows the battery voltage, which of course isn’t much use on LiFePo4. I’d love to have the equivalent of this external meter built into the 705; apart from being one extra thing to carry it doesn’t retain the counter values once unplugged.
I was always under the impression it was 50% - 80%, but sources vary. The generally accepted self-discharge rate appears to be 2% per month, so if storing for longer than a few months, then a higher storage percentage level would be more appropriate.
Personally I use my iMax charger to reduce a full charge to what it considers to be storage charge. Charging the batteries back to full capacity has indicated the storage level is around 90%. For short periods between activations of a couple of months I tend to leave them fully charged and just top them up before going out up the hills. Using this method my 2018 vintage batteries currently have more than 94% of their original rated capacity when tested at the standard minimum 3V per cell / 0.2C rates.
