NiMH in my Perdix?

[tbone1004]

@tbone1004 Thanks! That's what I did when I first used the NiMh on the Petrel. Set it to NiMH. What I noticed though is the Battery Indicator stayed FULL even after 40 hours of use. I didn't want to chance it quitting during a dive so I replace the NiMh with a fresh one after 40 hours even if the indicator still showed full. Is yours the same? How many hours are you getting from a fresh NiMh?

I don't track hours between battery changes, but it does go to yellow and you've got 1-2 hours left. As soon as it gets off of green, I change it, but I have definitely seen it yellow, red, and flashing on NiMH

 

[Rred]

Battery chemistry is a funny thing. I have had brass straps in dive lights literally turn black (and the contacts won't conduct) after alkaline batteries generated gasses over the long term. Any kind of battery can generate gasses, or just outright leak.

NiMh and NiCd are also ~1.25 volts when freshly charged, as opposed to 1.5~1.6 for new alkaline cells, and some equipment doesn't like that difference. Other equipment doesn't care. Then there are lithium primary cells (not LiOn, but primary) which are really great, but have different internal resistance and THAT's enough to upset some circuitry.

Bottom line, is to either follow the equipment maker's instructions (preferably checking to see if it was their techs or their attorneys who wrote them) or to experiment and go with what works.

One thing I've found is that using silicon high-dielectric grease on ALL electrical contacts can be a lifesaver. Prevents oxidation, prevents corrosion, and if something does leak? The crud just wipes off with the old grease. $5 will buy a huge tube sold as "silicon brake grease" in any auto parts store. Or a little 1/2 ounce tube as "o-ring grease" in any dive shop. Either one will do.

 

[tbone1004]

@Rred shearwater states NiMH is perfectly fine in their computers, as are any of the other AA form factor batteries out there

 

[Aloha Joe]

Even sealife strobes have vented caps. I hadn't thought about it until this thread, but a opv is something shearwater could add in order to improve things. They could put it in the little battery cover so users could upgrade to a vented cap, too.

Obviously not many people (if any at all) have had a problem with battery venting or the computers would likely already have a opv.

Strobes use short blasts of high current, and likely don't know when the battery is too low to be able to handle that current demand - which is a function of battery health as well as technology. So it's quite possible for a strobe to over-discharge a battery. On the other hand, the Perdix uses a constant but much lower current, and also has the ability to monitor battery voltage - it makes changes to the way it operates when it's low (adjusts screen brightness, e.g.) and may turn off or not operate below a certain point. Therefore the chance to significantly over-discharge a battery to the point of gas release is extremely unlikely.

 

[Rred]

Joe-
"Therefore the chance to significantly over-discharge a battery to the point of gas release is extremely unlikely."
As a practical matter, gas release only happens when a battery is OVER charged. Discharging it will not trigger a gas release. So unless a device is built to allow the batteries to actually be CHARGED while they are still inside it? Overpressure relief in the case makes no sense at all, wrt batteries.
On the other hand...folks have done things like open and close a sealed case while at altitude, and then been unable to open it up again when they got back down to sea level. It could be the pressure relief is some designer trying to make sure a case that was sealed at sea level, doesn't burst its seals when taken on aircraft. Not a battery issue at all.