ORIGINAL: rcairflr
This is discussed over and over again here on RCU. New Nimh packs need to be Form charged at C/10 and discharged at C/5 for 2 to 3 times (while monitoring the pack intermittently for heat) before fast charging. Below is from Hangtime Hobbies website, his business is batteries.
Q: What's up with 'Formation Charging'? Can't I just charge and fly a new pack?
A: The term 'Formation Charging' describes the initial charge/discharge 'forming' process that fully activates the 'chemical engine' and balances the cells in a new pack. NiMH packs have a particular need for repetitive c/10 charge/cycle conditioning, a 'break-in' procedure needed to get them to full rated capacity. Both NiMH and Nicad packs benefit from the process and the intent is to make sure that any new pack has been verified to be fully operational and that a 'start-up' capacity number is established for the pack before it's put into service. To 'Form' a new NiMH pack do three 10% 16-24 hour charges followed by a 300 to 500 ma discharge routine between each charge. In other words: Do a slow charge at the slow charge rate (or as close to it as you can reasonably get with your equipment) as shown on the pack label. Charge till the pack is warm, followed by a controlled discharge with a cycler. Do it 3 times. The recommended Formation Charge/ Slow Charge rate for our packs is printed right on the label of the pack as well as on the data card the pack was shipped with. New Nicad packs should get at least one slow charge followed by a 300 to 500ma discharge. Record the capacity numbers reported by your equipment for comparison cycling as the pack ages. Never check your brain at the door! As one respected modeler put it, "There's nothing more suspect than a new battery pack." Before you fly anybody's pack be certain it's fully operational and safe to fly.
The above says to do this to reveal a bad battery before trusting your equipment to it, as well as maximizing capacity and longgevity.
However, not doing this should not
cause a battery to vent. If you have a defective cell a forming charge may reveal it without the cell venting, therefore a safer way to go. But charging without forming shouldn't cause a good cell to go bad and vent.
My first charger didn't even have a slow charge option. I'm not saying this was a great setup or even that it is good for the batteries. However, I have never had a Ni-MH battery fail on me like
clamber's did. Some Ni-MH batteries even say not to trickle charge them right on the package. Not saying that they are correct, but I don't think they could say that if all their batteries overheated and vented when fast charged without a slow forming charge.
Having said all that, all batteries have a maximum safe charging amperage. I would check with the manufacturer to find out what the maximum safe charging rate is for that battery (and any others you might buy to replace that one).
Edit: By the way, I'm not saying that you shouldn't do a forming charge on a new battery. It is safer and better for the battery. I just don't think that not doing it should cause a battery to vent unless there was something else wrong with the battery.