I have a few old NiHM packs I picked up a few years ago and never really used. I'm trying to get my CVL completed, and pulled out the old batteries, but they are behaving funny. I don't know if it's my cheap chargers or what. I think they may have "gone bad" on me, but I don't know enough about battery technology to say for sure. Is there a known issue with NiHM batteries going bad if they aren't used/cycled often enough? They're essentially brand new batteries, that have been sitting in a box for about 4 years.
Yup. Cells do degrade over time even if not used. One thing I have noticed about MiMHs is the older they get, the harder it is to get the charger to start charging. I don't know if it is because the peak chargers are reading a higher starting voltage from the cells or just plain higher internal resistance. Perhaps someone more knowledgable may know. Back in my r/c car racing days when Nimhs were new technology in that hobby, we worked around this problem by taping down the start buttons to keep the charger running (Tekin chargers). After about 10 minutes, we would pull the tape and the charger would charge the battery normally. Of course if someone forgets to pull the tape, then the cells tend to overcharge and vent. Ask me how I know. Up until switching to LiFE cells two years ago, I would "pre-charge" the Verite's NiMH packs on a timer driven mechanical charger, then top off the cells with a peak charger. Another trick was to add a cell to the cell count in the peak charger's settings, i.e. battery pack has 5 cells, set charger for 6 cells. Ultimately though, 4 - 5 year old NiMHs are not going to perform well. They won't be able to carry a load without the voltage dropping excessively. They would be fine for cruising around, but you should consider newer batteries for battling. Before giving up on them, try to cycle the cells 5 - 10 times if they are literally never used before. New NiMHs need cycling to break them in and realize their full capacity.
OK thanks. I definitely need new/more batteries anyways. I picked up these two packs to experiment with, even if they are good to go, I don't have enough to battle with. They have never been in the water, I only ran the motors a few times with them on the bench, so they have cycled a few times but never really been under load. I did finally manage to get one of the packs to start charging, and charged until the LED on my charger went green. Perhaps it's a matter of kicking them a few times to start charging like you suggest. I'll try to charge the second pack now, the first one is hooked up to the ship and running motors at the present to see if they seem to fall away. Until I can get the ship in the water though, I don't really know what they're going to do.
I ran that first pack for over 2 hours until the transmitter died and the motors started racing wide open when the TX went dead. Hopefully that's a good sign that the packs are still usable. The second one seems to be charging now, before it was kicking the charger into a blinking red light which usually means the battery isn't chargable. Tomorrow I might throw it in the bathtub and run it under load to see how the batteries stand up.
Another question: I was planning on running two NiHM packs together to power the drive and the pump. Essentially, I have two Y harnesses connected together with two batteries on one side, and pump and ESC -> motors on the other. Am I going to have problems with the two batteries draining unequally and causing problems?
As long as the batteries are fully charged at the same time, there shouldn't be any real problems. There is a remote chance that one battery pack might not have the capacity of the other pack which may cause the low pack to drain too low and reverse polarity its cells. Before that happens though, the ship will most likely slow to a crawl and sink because the pump doesn't have enough voltage to pump well.
Yes, my plan was to keep the different packs as matched sets. Both of the ones I have presently are identical, and any extras I pick up will be in matched pairs for that reason.
Well, you don't expect them to perform in their optimum level actually. And if you have not stored them in the proper charge levels, you must have lost a few power with it. Though if it has not been a victim of memory problems, then you just have to cycle it out a few times and see how things are going to keep up with what you need. Hope that helps you out with it.
