Papa Tom

Cygolite recommends that I store my Metro 850 Headlamp and my HotShot 150 Blinkie for the winter at 30% charge. OK, so can anybody hit me with a set of steps to get my batteries to 30% and to KNOW when I'm there?

dsbrantjr

Well, you could get one of these West Mountain Radio - CBA HR but it is kind of costly just for bike light batteries...
Or you could charge them, record the time it takes to run them flat, recharge them and run them for 70% of the run-flat time and put them away. Which is kind of the same idea but cheaper.
What did Cygolight say when you asked them?

Papa Tom

It was kind of a challenge getting a definitive answer out of Cygolite. They suggested that I charge it for an hour; however, they didn't advise what my starting point should be...an hour from a totally discharged state? An hour from any state it's in when I put it away?

I know this is an almost impossible question to answer, but if there IS an answer out there, I figured this group would have it.

ThermionicScott 

Does this particular model change the color of the button's light (or blink) when it gets low?

Bill Kapaun

There's only 1 reference point. Any state of partial discharge is going to be nebulous.
I wouldn't "totally" discharge it, but if you are at the point the light is getting noticeably weak, you aren't that far away from totally discharged.

The rate of charge tapers as the battery voltage rises, since there is less potential for current to flow.
Think of a cell phone or similar device with battery level "bars".
Going from 1 bar to 2 is quicker than 2 to 3 is quicker than 3 to 4....

I guess you could read the voltage with a voltmeter at totally discharged & fully charged and interpolate 30%.

DiabloScott

You probably can't get in there with a volt meter, so that's out.
Cygolite is probably just pulling that 30% figure out of its USB port, so it's not that precise.
Full discharges frequently are not great for battery life, but occasional full discharge will be fine.

I suggest this protocol:
1. Charge it all the way to the max.
2. Discharge it all the way to nothing, using max output - time how long it takes to die.
3. Charge it all the way to the max again.
4. Discharge it at max output for 2/3 as long as the result in item 2.
5. Put it away for the winter.

ThermionicScott 

Actually, I think you're misinterpreting Cygolite's advice. I don't think they're saying to drain it to exactly 30% for storage, that's the minimum recommended charge. I would just top it off and call it a winter:

N.B.:

Papa Tom

My initial instinct was to keep an eye on them between November and April and just re-charge them once or twice during that time. In fact, that's what I did last winter. However, that was before I knew how much I liked these lights.

Bill Kapaun

Maybe charge it, use it every 2-3 weeks, repeat.

CliffordK

New recommendation?

I've always heard to top of the batteries.

Batteries, and devices will have a slow rate of self-dischage. So, if one charges to 30% in November, by March, it could be down to 10%, and dangerously low.

Storing it drained, or nearly drained is really bad on the batteries.

2old

If it's a Li battery, you shouldn't store it fully charged although that's better than discharged which is horrendous. Tesla is able to provide an eight year (or whatever) warranty on their batteries by allowing them to be charged to 80% and shutting down at 20%. If you can't locate a voltage vs SOC charge for your batteries, I'd store them at their nominal voltage. For instance: my 52V batteries charge fully to 58.8V; usually I store them at 52V which is 60% SOC.

Papa Tom

The batteries in these lights are not made to be removed, and that's part of the problem. If I could easily take them out without risking damage to the casing, I could test them every month or so and not have to lean on this group for advice.

Spoonrobot 

30% is not a hard number you need to meet, basically you just want to be under 50%, probably. Any closer to target and you're looking at stressin' about 1-3% capacity difference. Temperature is as important as charge state. Based on the specs online; run the 850 for 1 hour from full charge on high and the 150 45 minutes from full charge on high solid mode. Then put them in the fridge and consider them stored until you need them next year.

I used to use a Maha charger to discharge my batteries for storage but found little difference than just estimating capacity based on prior runtime from full charge and storing them in the fridge.

https://batteryuniversity.com/learn/...tore_batteries

FWIW the 850 is just a 18650 cell in a proprietary cover. You can open it up and replace the battery if you're comfortable with minor soldering/desoldering. The 150 is proprietary and does not appear to have any simple replacement alternative.

ThermionicScott 

Hmm, based on this I may need to take what I said earlier, @Papa Tom. Seems risky to store a battery at such a low SoC since it's bound to self-discharge a little over time, but Lithium-ion is weirder than the batteries I grew up with!

Thanks for posting this, @Spoonrobot. I've bookmarked it for future reference.

Papa Tom

Yes, good info, Spoonrobot. Thank you!