Yesterday I completed my weekly 200 km ride. The first 125 km were into a strong 25 km/h headwind, which made the ride unexpectedly long and draining.
About 5 hours in, the battery of my Varia RCT715 died. As I was replacing it with the backup RTL515, I was greeted with a battery critical warning. I assumed this was a delayed message from the RCT715; because, as many of you know, some notifications get stuck in the queue, waiting for older ones to be dismissed. On top of that, Garmin doesn’t allow you to name your lights, and the notifications aren’t aware of multiple devices, so context is often lost.
The confusion didn’t last long. The RTL515 shut down almost immediately, showing me that it had actually been the one with the critical battery all along. I kept riding for about an hour a long stretch of remote gravel, without lights or radar, hoping this would give the RCT715 enough time to recharge in my backpack.
When I reached busy paved roads again, I re-mounted the RCT715, expecting it to last the final stretch. But then came a surprise: the inside of the backpack was hot, which could only mean one thing: the Varia had somehow powered on while charging. In the end, the battery barely lasted another 10km, probably due to heat-limited charging.
Throughout this time, I kept getting some Radar Error 05 messages, but I had no idea what they meant. The mystery cleared up only later when I tried to swap the lights again: turns out the RTL515 had also powered on after some time on charger. So I ended up with two radars active at the same time, conflicting with each other. To make things worse, the RTL’s radar antenna was pointed at me. That explained everything, but by then, it was already too late. I knew what to do: manually shutdown them them and charge both properly, but how can you turn off a Varia that’s already off.
At that point, darkness had already set in; there was no time left for troubleshooting. So I gave up on the “smart lighting” for this ride and rode the final 60 km without radar, on twisty, unlit backroads, relying solely on the one trusty $10 emergency taillight that I never leave home without. It’s never failed me before; and this time, it proved itself once again by getting me home safely.
I haven’t found any documentation or field guide for managing multiple Varia lights during ultra-long rides. Given that the UT800 front light lasts only about 2 hours, such a guide would be useful even for “normal” long weekend rides.
Can anyone point me to such documentation — if it exists?
If not, let’s share what we’ve learned and maybe build an informal “long ride playbook” for managing Varia lights and radars safely and reliably.
We might even have a trick here:
Although Varia lights normally power off when connected to a charger, based on observed behavior, if the battery has gone completely flat, the device will auto-restart once it receives enough charge. This means it can potentially keep operating while powered by an external battery, as long as charging starts after an emergency shutdown. Could this behavior be used to our advantage on long rides?
For rear lights, this might be a way to extend runtime without carrying multiple units and without constant intervention.
Of course, this won’t work for front lights like the UT800, since their power draw exceeds what typical power banks can provide to a device that doesn’t support fast charging.
P.S.:
I’m still not sure why the RTL515 was already drained when I first tried to use it. It’s something I need to investigate. Since it’s my backup light, I only take it with me on longer weekend rides. Maybe I partially charged it and forgot. Maybe the battery is degraded. But most likely, I passed near the unit during ride prep, it auto-powered on due to proximity with a paired device; and then stayed on unnoticed until it ran out.