Cave Diving Backup Lights / Rechargeable Batteries

[rjack321]

-once a year run a discharge test to confirm that they hold 90%+ (below this threshold the batteries get dangerous (what might happen exactly, overheating?))

Catch fire and burn your house or garage down. <90% capacity is time to move on to a fresh cell(s)

 

[tbone1004]

@sprockjohnson @tbone1004

so i got a second-hand lx20+ and it arrived with 4 xtars 3500mah 3.6v 18650 batteries and xtar mc4s charger

to best preserve the batteries i must:
-not store them fully charged, nor discharged (store with 50% ish charge)
-once a year run a discharge test to confirm that they hold 90%+ (below this threshold the batteries get dangerous (what might happen exactly, overheating?))
-is the mc4s charger good enough or its best a get a fancier one?
-should i remove the battery block from the light alltogether when stored?
-any other important steps i missed

Thank you

1-yes but sort of. they don't really care what SoC it is as long as it is within like 20-80% so the general recommendation is to put them away after a dive and only fully charge them just prior to a dive
2-essentially but depends on how you are doing your discharge test. IIRC the LX20+ will kick into low battery mode and drop down to low and will burn for a million years after it kicks into low *slight exaggeration but it's over 3hrs AFTER it kicks into low which makes doing a capacity test based on burn time impractical.
3-it's adequate. it doesn't tell you anything useful, but it's fine. For point 2, if you want data like that then get one with a tester function so you can just run a capacity test in the charger
4-flip it over for storage
5-not really? Depending on which goodman you have you may want to configure the loop on the back of the light with a bolt snap that can clip easily to the goodman handle itself so if them QRM comes undone it doesn't fall off and drop into the abyss. The magnetic switch can also be a bit weird if you dive in really high particulate water or it gets around too much sand so every once in a while it's not a bad ideal to disassemble the exterior part of the switch for cleaning, pretty sure that's in the manual somewhere?

 

[Underwater Tourist]

maybe a stupid question, but is it kosher to start charging the batteries the night before, and to leave them plugged into the charger for the entire night

so basically, i dive during the day, come home, charger them overnight, go diving in the morning

 

[Whitrzac]

Buy the vc8 plus. It can charge 8 at once and has a test/cycle and store mode on 4 of the bays. While costing the same as the vc4 and being a similar size

 

[tbone1004]

maybe a stupid question, but is it kosher to start charging the batteries the night before, and to leave them plugged into the charger for the entire night

so basically, i dive during the day, come home, charger them overnight, go diving in the morning

that's what most of us do, you don't want to store them at full charge for long periods of time but charging overnight to use the next day is perfectly fine.

 

[ACHiPo]

Buy the vc8 plus. It can charge 8 at once and has a test/cycle and store mode on 4 of the bays. While costing the same as the vc4 and being a similar size

I got the VC8+ and it’s a great charger. The instructions, however, suck. How long does it take to test/cycle a battery? I’ve had two in for about 6 hours and it still seems to be testing/cycling. Does test/cycle rejuvenate a battery that was stored full?

 

[inquis]

is the mc4s charger good enough or its best a get a fancier one?

A fancier one like the VC4 Plus has a storage mode -- the easiest approach. $33 at the moment.at Amazon. There are probably other places for cheaper.

https://a.co/d/edqtKZD

If you're technically inclined, you could use a multi meter to test the batteries. The target is about 3.7 volts for storage. Lower than that, charge for a bit and extrapolate when to terminate charging. Higher, you'll have to run the light in a bucket of water for a bit and extrapolate when to terminate the run. (You'll get a feel for the drain & charge rates in volts per minute.)

The cheapest option is to use the charger you have, which will charge just fine, but you'll then need to run the light in a bucket of water (or go diving!) for roughly half the burn time.

 

[tbone1004]

I got the VC8+ and it’s a great charger. The instructions, however, suck. How long does it take to test/cycle a battery? I’ve had two in for about 6 hours and it still seems to be testing/cycling. Does test/cycle rejuvenate a battery that was stored full?

depends on the battery and if you put it in full or empty. Has to fully charge, fully discharge, fully charge again. Discharge I think is around 0.3a so the discharge cycle alone could take close to 12 hours. Some of them are faster, but just budget 24hrs for a test cycle.
On a single cell of lithium chemistry the test cycle is inconsequential. On NiMH cells like eneloops though it can make a huge difference to run them through a full test cycle.

A fancier one like the VC4 Plus has a storage mode -- the easiest approach. $33 at the moment.at Amazon. There are probably other places for cheaper.

https://a.co/d/edqtKZD

If you're technically inclined, you could use a multi meter to test the batteries. The target is about 3.7 volts for storage. Lower than that, charge for a bit and extrapolate when to terminate charging. Higher, you'll have to run the light in a bucket of water for a bit and extrapolate when to terminate the run. (You'll get a feel for the drain & charge rates in volts per minute.)

The cheapest option is to use the charger you have, which will charge just fine, but you'll then need to run the light in a bucket of water (or go diving!) for roughly half the burn time.

The voltage curve is too flat to get much useful data without an extremely expensive multimeter that can measure at least hundreths of a volt. Anything under 3.5v and you should probably charge it, but anything above 3.5v is probably good enough.

 

[inquis]

How long does it take to test/cycle a battery?

Depends on the battery. Charge is probably at 500 mA (though could be higher), and discharge is at 300 mA. For a 3400 mAh battery from half-full, I'd expect more than 22 hours. (The charge rate tapers off as it gets full.)

Does test/cycle rejuvenate a battery that was stored full?

No, assuming you mean a lithium one.

 

[ACHiPo]

Depends on the battery. Charge is probably at 500 mA (though could be higher), and discharge is at 300 mA. For a 3400 mAh battery from half-full, I'd expect more than 22 hours. (The charge rate tapers off as it gets full.)

No, assuming you mean a lithium one.

Thanks. I gave up after ~36 hours and set the mode to “store”. The two Li ion batteries in question went into and stayed in store mode ok. The last time I used them they only lasted about 15 min, so I’m thinking they were flaky quality (they are Tenergy brand), or I killed them by charging them to full and storing them. I’ll pop them into a dog walking light and check them again.