PSA: Charge Your Bike Lights for Summer!

Hey! You! Yeah, you, with the nice bike and the telltale light mount on your bars and helmet! Remember those lights you trusted all winter to illuminate your journeys down twisted trails and over mucky roots? Daylight Savings was more than a month ago, and chances are that you’ve used those lights less and less over the ensuing weeks. So whenever you decide that night ride season is over, and evening-ride-with-no-lights season has begun, here’s your friendly reminder: Your lights took care of you all winter. Now it’s time to take care of them.

Short version: Before you put your bike lights away for the summer, charge them all the way up, inspect them for damage, and make sure you’re storing them in a safe, temperature-stable place. As an added bonus, make sure you have all the parts to their mounts, and consider storing those in the same place too so that next fall you’re ready to go.

We could just leave it at that, and if that’s all you read, you’re good to go. But, because I’m a nerd, who’s also got some nerd friends, I hit up Tom “Danger” Place of Outbound Lighting for even more info. In addition to being one of the guys behind the Outbound Evo DH package I reviewed and enjoyed, Tom knows a lot about lights. He’s got a sweet homemade custom light on his eBike that may or may not contain some wiring that he yanked out of a hotel room TV right before Sea Otter to make it work. He also is the creator and owner of a wild light-up helmet that looks sort of like Mario Cart’s Bowser on mushrooms. So yes, he knows a thing or two about lights. Tom went deep, I learned a thing or two, and maybe you will too!

We should fully charge lights before we store them. What's actually happening inside the battery over the summer that causes it to degrade?

All batteries have some level of self-discharge at their base level, typically low enough that leaving a bare cell sitting around is a non-issue for a long time, but it’s there. More important is the fact that all electronic devices connected to said batteries have some amount of quiescent current draw (otherwise known as vampire draw, phantom load, parasitic drain, all great metal band names, bad for batteries) where the microcontrollers/chargers/ICs all pull some very small amount of power continuously if the battery isn’t fully disconnected, which is impossible in a lot of modern electronics, like bike lights.

Even if your light (or cell phone for that matter, except you’re using that 24 hours a day so this never happens as there is no “cell phone season”) is OFF, it will drain the batteries at some slow rate. Properly designed electronics (like Outbound, for example) design their circuits to minimize this and measure the drain in microamps, so the effective “standby time” is well over a year, which means if you fully charge the light, it’ll take more than a year to completely self-discharge, so that a full season of storage is totally fine. Some less-well-engineered products have standby time measured in weeks. Keeping the batteries from sitting dead and draining further is paramount.

Does leaving batteries mostly uncharged really hurt the runtime in the future?

Not only can it hurt runtime, it can straight up kill the battery itself. All Li-Ion cells have an operating range of voltage of ~3.2V to 4.2V, and if the battery drains below the ~3.2V lower threshold too much, it will effectively result in a reduction of capacity, or in worst case you may not even be able to recover the cell at all, as most charge controllers have limits to the voltage it will allow cells to charge at for safety reasons.

What performance issues are you going to notice if you don't store your batteries fully charged?

Shit won’t work, that’s what. The fastest way to kill a Li-Ion battery is to leave it sitting dead for a while. We cover battery replacements for all our products for free and basically every single damn one we’ve ever had to replace has been because of improper storage. Only one dude actually used his light enough to warrant a replacement cell, and he’s nuts, you are not him. If you don’t charge your lights for storage, best case scenario is your runtime will go down over time, worst case it’ll just straight up die.

Don’t Li-Ion batteries have a finite lifespan where they’re just not good after a couple years anyways?

Yeah, if you leave them dead for months at a time, sure, but seriously no. Charge/discharge cycles (actually using them) will degrade capacity over time, but it takes ~1,000 cycles running full dead to full charge for most Li-Ion cells to see a modest ~20% reduction in capacity. That’s 10 years of using your light twice a week, or 3 years using it literally every single day, just to see a small capacity reduction.

Do you need to let your light run dead before recharging it?

Dude, no. This is a relic of NiCd battery chemistry where they had a “memory” if you didn’t discharge fully before recharging, Li-Ion cells do not exhibit memory, so it’s always best to just immediately charge your lights when you can, that’s always better than running them dead (which is OK to do of course, it’s just always better to minimize that time spent dead, just as in human life).

Why should we store them in a consistent temp area? Why are big swings bad for the batteries?

Two reasons: Lithium plating and thermal instability. On the hot side, the makeup of the cell itself can become unstable if it’s too hot, which is a safety issue, so smart chargers (almost every charger sold these days) will not charge above a certain temp so the cells hold all that stuff inside (has to be really hot, but still). 

More importantly for most consumers, on the cold side the lithium ion transfer is slowed significantly below freezing, which can lead to interactions that cause plating which reduces capacity, and in worst case complete blocking of energy transfer. Thermal shock going from one extreme to the other just exacerbates this effect. Keeping batteries in a garage when temps can be below freezing in winter and boiling hot in summer is just suboptimal, so keep all that inside if you can.

Any horror stories related to improper storage that you want to share?

Imagine if you will, a world where you’re about to embark on a journey on your bicycle at night. It is the middle ground between light and shadow, between science and superstition, and it lies between the pit of man's fears, and the summit of his knowledge. You open a door, it leads to your garage, where on a shelf you find your bike lights, cold, and alone. They’re dead. You press buttons, you plug in to charge them, nothing. The silence is deafening, the darkness, all encompassing, there is no response, nothing you can do before your friends arrive where you must admit: I murdered my lights. I ran them dead and left them many months ago. I cannot make the ride tonight.

The risk of fire is actually unbelievably ridiculously low, it just makes the news every time a Tesla goes up in flames (even though gas cars catch fire more often, but I digress), as the cells are well-made by only a few companies in the world and there are TONS of safeties in modern electronics, the only exception being vape pens that are just the worst for basically every other reason also. The far more likely event is that you’ll find your lights dead because you left them uncharged, worse in an environment with no temperature control, and now the cells are unrecoverable and have to be replaced entirely for the light to work.

TLDR: keep your shit fully charged, in stable indoor temperatures, and check in on it once in a while, and you’ll be good.