Am I overdischarging batteries in my bike lights?

[OpenGuy]

I've recently started using 3 L2D CE Q5 torches on my bicycle for the commute home. I use a variety of NiMH AA cells (in matched sets). The first time one light got low on batteries, it started noticeably switching between turbo and low modes, then I just switched off the lights one at a time to discover which one.

Tonight I put freshly charged batteries in two lights, but had no more charged batteries at work, so I was sort of expecting that the other light would run out of juice and was watching for any indications of variable light output. I didn't see anything until I got home, when I noticed this light was very dim. My commute is 25 minutes, so it could have been dim that long (it was bright when I first turned it on).

Questions:

How bad is discharging a battery like this? Just how hard should I avoid it.

Is there a more reliable way to determine when one light out of 3 has run out of juice? (Two running out would be very noticeable.)

 

[HKJ]

I would just replace all batteries after two trips. That way your avoid running the batteries dry and does always have some extra power.

 

[jirik_cz]

I would recommend recharging every day before trip. That would surely avoid overdischarging

 

[Fallingwater]

I would recommend recharging every day before trip. That would surely avoid overdischarging

Indeed. It'd also prolong the life of the cells. They like partial cycles better than full cycles.

 

[Hondo]

+2 to peaking the batteries each ride on a good charger.

Questions:

How bad is discharging a battery like this? Just how hard should I avoid it.

Is there a more reliable way to determine when one light out of 3 has run out of juice? (Two running out would be very noticeable.)

1. NiMH's do NOT like being deep cycled, good chargers that do battery cycling will stop discharging when the cell reaches 0.9 volts UNDER LOAD. They will take a fair bit of abuse, though, and you most likely still have good cells, but doing this regularly will significantly shorten their life.

2. Run your hand in front of the bezels? On turbo, if you can't see the difference in brightness that way, the cells are probably still plenty safe. But as above, daily topping (or every other day) will negate the whole issue.

 

[OpenGuy]

Thanks for all the responses. Daily recharging it is then.

 

[arpit]

Yes, the torch is badly designed, and over discharges batteries as a matter of course. Charging the batteries in a charger which monitors each cell individually will mitigate the problem to a certain extent.

 

[HKJ]

the torch is badly designed, and over discharges batteries as a matter of course.

Like nearly all equipment that uses AA batteries it can work with alkaline batteries and that prevents any battery protection circuit (Alkaline has a rather low output voltage under heavy load).