Hi, folks! I recently bought a bunch of 7.2v 3800mAh battery packs from www.all-battery.com. My usual battery charger is a Triton, one of the best computerized chargers on the market several years ago. The trouble is, when I cycle the batteries (fully discharge then fully charge) to double-check their mAh rating, my charger is only putting in about 3100 mAh of charge. So, I've got several questions. First, does anybody have any idea why my charger is putting in 800mAh less than it's supposed to, and what I can do to fix it? Second, I'm considering switching to a trickle charger, to see if that will get me up to a full charge. I've got 8 battery packs to charge, so one of the things I've been considering is to wire up all the batteries in parallel so I can trickle charge them all at once. Is this advisable? If not, are there any really cheap trickle chargers that I can buy in bulk?
couple of options: the charger is no longer calibrated properly and is either discharging more than it thinks it is or it is not reading the low voltage cutoff properly. The batteries really are not 3800mah. I have seen this too, usually with cheap cells. Or the cells are getting old.. or were discharged to zero volts, or damaged via overcurrent, etc. the other option is that you have the charger set to the wrong chemistry and it is peak detecting early (or you have the peak set to low, if that setting is available). Your best bet is to find someone else with a charger that can check for you... if they both show similar readings, then it is the batteries, if not, it is your charger
I looked at the settings on my charger again. It was set to NiMH, 0.5A discharge to 0.5A charge cycle, 3mV/cell peak. I've change it to 0.5A discharge to 0.3A charge cycle, 5mV/cell. These are new packs, so it may be that they need to be cycled a few times and the peak was set too low. Since they are 3800mAh, I'm charging at 0.3A, which is a bit less than 1/10C. I'll let you know how it went in about 19 hours when the cycle is complete.
I posted a response to the question separately in the Big Gun forum. The short of it, is the first charge or two should be at a low rate. C/10 (battery capacity divided by 10) is the universally accepted rate of charging without damage. It also ensures a complete charge. New packs most of the time will be out of balance in that one cell has more juice than another one. A trickle charge at C/10 will allow those cells to balance out. Keep in mind this is just talking about NiCAD and NIMH (technically SLA falls into the balance part as well), since LiPoly requirements for balancing are different. With packs that have been stored for a while, it can take 2-3 low discharge/low charge rate charge cycles to get them back at full capacity. In fact a non-smart trickle charger performs well to get those back up to their rated voltage before trying to tackle them with a smart charger that sometimes will mis-detect the cell count or will detect a fault on a completely discharged pack. Nothing wrong with just trickle charging. It's a good way to make the packs last longer, just don't leave them on there longer than needed as it will reduce the capacity after a while.
